Segmented phase shifter

Abstract

In some implementations, a photonic integrated circuit (PIC) can include a plurality of input ports to input light, such as quantum light (e.g., single photons) or bright light. In addition, the PIC may include a waveguide network that includes a crossing network to interfere the light. The light can be phase shifted using segmented phase shifters. The photonic integrated circuit can further include output ports to output the light.

Description

CLAIM OF PRIORITY

[0001] This application claims the benefit of priority to U.S. Patent Application Serial No. 63 / 615,112, filed on December 27, 2023, which is incorporated by reference herein in its entirety. TECHNICAL FIELD

[0002] The present disclosure relates generally to optical devices and more particularly to phase shifters for quantum photonic interferometers. BACKGROUND

[0003] Mach-Zehnder interferometers (MZIs) are optical devices that consist of two beam splitters and two mirrors that allow a light beam to be split into two paths and later recombined. MZIs exploit interference effects between the light beams traveling in each path. By modulating the relative phase shifts between the two paths, the output intensity of the recombined beam can be varied.

[0004] Generalized Mach-Zehnder interferometers (GMZIs) include additional optical components in the two paths, enabling advanced manipulation of the beam, BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The following description includes discussion of figures having illustrations given by way of example of implementations of embodiments of the disclosure. The drawings should be understood by way of example, and not by way of limitation. As used herein, references to one or more "embodiments" are to be understood as describing a particular feature, structure, or characteristic included in at least one implementation of the inventive subject matter. Thus, phrases such as "in one embodiment" or "in an alternate embodiment" appearing herein describe various embodiments and implementations of the inventive subject matter, and do not necessarily all refer to the same embodiment. However, they are also not necessarily mutually exclusive. To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure (“FIG.”) number in which that element or act is first introduced.

[0006] FIG. 1 shows a first example optical switch, in accordance with some example embodiments.

[0007] FIG. 2 shows a second example optical switch, in accordance with some exampie embodiments.

[0008] FIG. 3 shows a third example optical switch implemented as a GMZI, in accordance with some example embodiments.

[0009] FIG. 4 shows an example GMZI configured as a N-to-1 multiplexer configuration that implements a plurality of phase shifters, in accordance with some example embodiments.

[0010] FIG. 5 shows an example linear-optical quantum generalized MZI in a 16x16 configuration, in accordance with some example embodiments.

[0011] FIG. 6 shows an example GMZI architecture, in accordance with some example embodiments.

[0012] FIG. 7 shows a GMZI switch architecture, in accordance with some example embodiments.

[0013] FIG. 8 shows close-up view's of example components of a photonic integrated circuit (PIC) based GMZI, in accordance with some example embodiments.

[0014] FIG. 9 shows a quantum GMZI architecture in a balanced configuration in which the optical powers across the network are equivalent, in accordance with some example embodiments.

[0015] FIG. 10 show's the first Hadamard network of FIG. 9, in accordance with some example embodiments.

[0016] FIG. 11 shows an example segmented phase shifter, in accordance with some example embodiments.

[0017] FIG. 12 shows a GMZI layout incorporating an array of segmented phase shifters, in accordance with some exampie embodiments.

[0018] FIG. 13 shows a detailed view of one of the segmented phase shifters of the GMZI layout of FIG. 12, in accordance with some example embodiments.

[0019] FIG. 14 shows a flow diagram of a method for processing light using a GMZI, in accordance with some example embodiments.

[0020] FIG. 15 shows a flow diagram of a method for processing quantum light using a GMZI, in accordance with some example embodiments.

[0021] FIG. 16 show?s a flow diagram of a method for calibrating an array of segmented phase shifters of a GMZI, in accordance with some example embodiments.

[0022] FIG. 17 show's a flow diagram of a method for adjusting the phase of light in a waveguide arm of the GMZI using a segmented phase shifter, in accordance with some example embodiments.

[0023] FIG. 18 shows a flow diagram of a method for processing quantum light using a GMZI having segmented phase shifters, in accordance with some example embodiments.

[0024] Descriptions of certain details and implementations follow, including a description of the figures, which may depict some or all of the embodiments described below, as well as discussing other potential embodiments or implementations of the inventive concepts presented herein. An overview of embodiments of the disclosure is provided below, followed by a more detailed description with reference to the drawings. DETAILED DESCRIPTION

[0025] In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide an understanding of various embodiments of the inventive subject matter. It will be evident, however, to those skilled in the art, that embodiments of the inventive subject matter may be practiced without these specific details. In general, well-known instruction instances, structures, and techniques are not necessarily shown in detail.

[0026] A generalized Mach-Zehnder interferometer (GMZI) can be integrated in photonic integrated circuits for various quantum photonic and optical communication operations. A GMZI may be implemented using splitter networks and phase shifters to perform routing of light. In some cases, the light routed by the GMZI is quantum light. As used herein, the term quantum light include one or more of the following: a single photon, squeezed light, or an entangled photonic state (e.g., Bell pair, Greenberger-Horne-Zeilinger (GHZ) state). In some cases, the light routed by the GMZI is bright light (e.g., thermal light, classical light).

[0027] The splitter networks may comprise sets of couplers, bends, and crossing couplers to couple the light. In some embodiments, a first coupler network separates the light, and a second coupler network combines the light onto one or more output ports. In some embodiments, between the coupler networks are phase-shifter elements (e.g., a first phase shifter for switching, a second phase shifter for trim and calibration) to change a phase of the light on a given arm of the GMZI such that the light is configured according to a transfer matrix and output from the GMZI in various configurations, such as an N-to-1 configuration or an N-to-M configuration, as discussed in further detail below.

[0028] In some example embodiments, a GMZI may accumulate unwanted phase changes (also referred to herein as phase error) that build up on the various components, such as the X-couplers in the GMZI's Hadamard crossing networks. The phase error can occur due to various factors, such as process variations of the components or surface roughness. In some cases, the 50:50 splitters used in the GMZI can also contribute to decreases in phase accuracy and therefore to phase error. The phase error can affect GMZI performance and cause inaccurate phase shifting.

[0029] In some example embodiments, the segmented phase shifters may be configured to operate in two stages. During a calibration stage, the unwanted phase changes associated with a given path from an input to an output are identified (e.g., intensity measurement of bright, light coupled to the input and measured at the output), and a subset of the phase shifter segments along the waveguide are activated to negate the phase change. During an operation stage, the phase shifter segments can be selectively activated and / or deactivated, as necessary, to effect real-time fast phase shifting to a target phase value; for example, to effect fast n phase shifts in real time.

[0030] In some example embodiments, the segmented phase shifters operate according to binary states (active / inactive) for each phase shift segment. The segmented phase shifters may include phase shifter segments effecting different amounts of phase shift: for example, some segmented phase shifters may include one or more coarse phase shifter segments effecting a relatively large amount of phase shift (e.g., four segments each effecting 2rJ5 radians of phase shift when activated) and one or more phase shifter segments effecting a relatively smaller amount of phase shift (e.g., four segments effecting 2te / 1 0, 2k / 20, 2jc / 40, and 2k / 80 radians of phase shift, respectively, when activated). In some example embodiments, the segmented phase shifters may include phase shifter segments effecting the same amount of phase shift (e.g., five segments each effecting 2% / 5 radians of phase shift when activated). In some example embodiments, the total amount of phase shift that can be applied by activating all of the segments of a segmented phase shifter is equal to, or close to, 2u. In some example embodiments, the total amount of phase shift that can be applied by activating all of the segmented of a segmented phase shifter is greater than 2%, and only the portion of the segments of a given phase shifter that yield a 2tt shift in a given circuit design are implemented for calibration and real time phase shifting (e.g., the segmented phase shifter comprises a surplus of segments to ensure a shift is achievable in various circuit designs and to compensate for different manufacturing variations).

[0031] FIG. 1 shows an example optical switch 100, in accordance with some example embodiments. The optical switch 100 (e.g., an MZI) comprises a first splitter 105 (e.g., a beam splitter, half silver mirrors, a directional coupler, a multimode interference (MMI) waveguide, a cross coupler or “star” coupler) and a second splitter 110 (e.g., a beam splitter, a crystal, half silvered mirror, a directional coupler, an MMI) that separate the light (e.g., bright light or quantum light) onto a top arm and bottom arm and then recombine the light for output on one or both output ports. In the example of FIG. 1, the top arm comprises an active phase shifter 115 and the bottom arm comprises an active phase shifter 120. Further, the bottom arm comprises a further fixed passive phase shifter 125.

[0032] In FIG. 2, an optical switch 200 comprises the first splitter 105 and the second splitter 110 that separate the light onto the top and bottom arms and then recombine the light for output on one or output ports. Further, in the example of FIG. 2, the optical switch 200 comprises a single active phase shifter 130 on the bottom arm to implement ?r phase shifts.

[0033] FIG. 3 illustrates an optical switch 300 implemented as a generalized MZI (GMZI), in accordance with some embodiments. The GMZI is an extension of an MZI with N > 2 inputs 317 and M > 1 output ports 319, as shown in FIG. 3. This configuration allows a set of permutations to be performed on the inputs 317, thereby configuring the optical switch 300 as a useful block in the design and construction of composite N-to-1 and N-to-M switch networks. In some embodiments, varying the settings of phase shifters 310 (e.g., active phase shifters) sets specific permutations of the N inputs 317 and routes them to M > 1 output ports 319. There are a number of spatial mux schemes that select one of multiple inputs 317 from distinct locations in space. For example, a GMZI can be configured as an N-to-1 mux, as it allows routing of any input 317 to a single output port 319.

[0034] As illustrated in FIG. 3, the example GMZI comprises a first Hadamard network 305 or splitter (e.g., an MMI, a network of directional couplers and waveguide crossings) and a second Hadamard network 315 or splitter (e.g., an MMI, a network of directional couplers and waveguide crossings) that spiit and recombine the light propagating on one or more of a plurality of arms (e.g., eight arms, in an 8x8 GMZI) such that the light is outputted on one or more of the plurality of output ports 319. Example architectures for the first Hadamard network 305 and second Hadamard network 315 are discussed in further detail below.

[0035] In a bright tight example, the optical switch 300 can operate as a power splitter that splits the beam onto the output ports 319 in a given configuration according to settings of the phase shifters 310. In quantum light operation (e.g., propagating one photon or a small number of photons), the optical switch 300 splits superpositions of the quantum light onto the output ports 319 for recombination and output according to settings of the phase shifters 310.

[0036] FIG. 4 shows an example GMZI 400 configured as a N-to-1 multiplexer configuration that implements a plurality of phase shifters 405, in accordance with some embodiments. The GMZI 400 is an example configuration that can collect light (e.g., bright light, quantum light, single photons) from a plurality of optical sources that generate the light with a probabilistically low7 occurrence to output a single muxed source of light (e.g., muxed quantum light) with a probabilistically higher occurrence. The configuration of the GMZI 400 is an example of an optical switch as previously described (e.g., optical switch 100, optical switch 200, or optical switch 300).

[0037] FIG. 5 shows an example linear-optical quantum generalized MZI 500 in a 16x16 configuration, in accordance with some embodiments. The coupler network 505 corresponds to the first Hadaniard network 305, and the coupler network 515 corresponds to the second Hadamard network 315, which together function as a 16-mode Hadamard quantum optical coupler network. In some embodiments, the plurality of phase shifters 510 are implemented as phase shifters that can be set from zero to ?r shifts to select one of 16 operations (e.g., G([2, 2, 2, 2]). In some embodiments, each phase shifter on each arm comprises a plurality of phase shifters, as discussed in further detail below. Further, the linear-optical quantum generalized MZI 500 is an example optical switch that may be used to route quantum light by configuring the phase shifters 510 in different permutations.

[0038] In quantum photonic implementations, a Mach-Zehnder Interferometer can be configured to apply identity or swap operations on two inputs. For example, to switch between transfer matrices which are pairs of Pauli operations using active phase shifters: I or X ------ h(I or Z)h ------ Shc(Z or I or F ::: Sh(I or ZihS ------ Zhc(Z or J)hc (1   1 \              / 1   _ A                   / fj  1\ ] / V2, hc = (       ] / ^2 , and X = (     ] 1 —1 /                1 /              \1 0 / / 0 -A      / 1 0\ , Y -        ), Z - [ I v 0 J     \0 ij

[0039] As such, the GMZIs can be configured to function as a switch network that implements a set of unitary transfer matrices Uk, where each unitary routes light between a subset of input and output ports. As an example, if Uk is set to route light from port t to port s, then its sih row and tih column are set to zero apart from \U«,t\ = 1, and similarly for other pairings of input and output ports. The following elucidates example sets of routing operations of a photonic GMZI switch-based information processing architecture, in accordance with some embodiments. In some embodiments, the photonic GMZI switch-based information processing architecture is configured as a scalable waveguide-based switching network that implements transfer matrices using interferometer gates and phase shifters. In some embodiments, the transfer matrices are of the form: __ jy p yt, where the unitary matrices W, Kdescribe passive interferometers, and the Dk form a set of diagonal phase matrices (e.g., phases applied by the phase shifters). In some embodiments, the phase matrices are implemented physically using a single layer of phase shifters acting on every waveguide arm, while in some example embodiments, each arm comprises a plurality of phase shifting units. In some embodiments, the slow' phase shifters are used to zero out a given photonic device.

[0040] In the following, the phase matrix -^is implemented in terms of a phase vector d,            for simplicity. In some embodiments, the photonic GMZI switch-based information processing architecture is configured to function as a scalable switch network that implements different sets of permutation matrices _ jy yt, according to desired routing configurations. By adding the fixed passive network (e.g., a Hadamard network) corresponding to, e.g., U"1 (e.g., the inverse of an arbitrary permutation from that set), anew' set of pairwise commuting permutation matrices: IV - & - 1 " (“^)} =            _ (k ) VK " t} may be generated. At a high level, and in accordance with some embodiments, the photonic GMZI switch-based information processing architecture is configured as a switch network where           j - (-1)} = {W -¾ W1!} is a set of transfer matrices corresponding to commuting permutations of N waveguide arms or modes (e.g., N == 4 in FIG. 7) for a given switch network configuration. The individual phase shifter settings in Dk correspond to given roots of unity (e.g., up to an overall global phase factor which can be chosen at will). Further, the photonic GMZI switch-based information processing architecture implements one or more GMZI switches with a switch setting Dk to route light from input port 1 to output port k.

[0041] The embodiments below illustrate example linear-optical photonic circuit GMZI architectures to implement different routing operations G([ni, ns, ■ • • , nr]) on waveguide arms n = IT nr (( x\        /   /  \\                /   /  \\ ® fJ ®... ® ICM with settings vector k where 0 < ki < m with / 1,--, / -, and further where the transfer matrices jyt are as follows:

[0042] In the above transfer matrices, the Wr‘! are discrete Fourier transform (DFT) matrices and the Jkh setting of the fast phase shifters are set by: with (d^) =e :2~' ' " fw D,"

[0043] In some embodiments, scalable networks of GMZI switches are implemented to a large number of modes or waveguide arms, N, with logdepth stages of interference using the following decomposition:

[0044] In the above decomposition, the matrices Sv correspond to crossing networks (e.g., the crossing network crossing network 1020, shown in FIG. 10) which reorder modes in waveguides in the GMZI. In some embodiments, the subexpressions of the form           0 wn‘ correspond to repeated blocks of modes interfering according to unitary in the above decomposition, and thus function as stages of local interference separated by crossing networks, such as the crossing network 1020 (FIG. 10). Further, FIG. 5, discussed above, illustrates an example of a Hadaniard GMZI implementing the N-M decomposition (e.g., spectral decomposition into submatrices that correspond to physical components), and FIG. 4 illustrates an example of the Hadamard GMZI implementing the GMZI as a simplified N-to-1 mux.

[0045] In some embodiments, additional GMZI architectures are implemented by decomposing the unitary matrices VF"' that set the design of beam-splitter operations (e.g., the first Hadamard network 305 or the second Hadamard network 315) and phase-shifter operations (e.g., phase shifter 310). It is appreciated that the optical depth of networks constructed using the recursive decomposition is reliant on high-precision optical hardware and very low7 optical loss, as the depth of the crossing networks must be accounted for in addition to the stages of local interference (e.g., the depth in crossings of the largest crossing network scales with (N / 2)-l).

[0046] FIG. 6 shows an example GMZI architecture 600 in accordance with some embodiments. In the example of FIG. 6, a plurality of waveguide arms input light (e.g., bright light, quantum light) into a first Hadaniard network 610. The output light from the first Hadamard network 610 is then phase shifted by a plurality of phase shifters 615 and input into a second Hadamard network 620. In the example configuration of a GMZI architecture 600, a single layer of the phase shifters 615 are implemented to perform phaseshift-based light mixing (e.g., bright light mixing, quantum-light probabilitydistribution adjustments). In some example embodiments, the phase shifts applied comprise 0 to ?rphase shifts and zero to 2?r phase shifts. In some embodiments, the phase shifters are operated in an “in-between” phaseshifter configuration to act an array of beam splitters. In these in-between configuration embodiments, light is input into two target input waveguide arms and can be interfered with 50% of the light transmitted to a given output port where the measurement is made (e.g., via photodetector). In some embodiments, a set of phase shifters are implemented on each arm, as discussed in further detail below.

[0047] Continuing, with reference to FIG. 6 and in accordance with some embodiments, the light adjusted by the second Hadamard network 620 is outputted from the second Hadamard network 620 (e.g., from the right side of the second Hadamard network 620 in the perspective view of FIG. 6) to one or more detectors 625. Although the example of FIG, 6 shows eight waveguide arms (e.g., eight modes, N 8). it is appreciated that in other embodiments different numbers of waveguide arms may be implemented in a similar manner.

[0048] In some embodiments, the one or more detectors 625 are singlephoton detectors (e.g., photon-number-resolving detectors) that detect a single photon of light as the photon exits the second Hadamard network 620. In some embodiments, the photo detectors are bright-light, detectors (e.g., phototransistors, photodiodes) that are implemented to detect bright light that is power split onto the plurality of outputs of the second Hadamard network 620. For example, in some embodiments, bright light is injected into one of the input ports of the second Hadamard network 620 and is detected from one of the output ports of the second Hadamard network 620, wherein the phase shifters 615 are calibrated by modifying the phase shift, settings until the phase difference between the input, light and the output light is minimized or zeroed out. In some embodiments, a portion of the output bright, light is tapped from the output waveguides of the second Hadamard network 620 to perform the bright-light-based adjustments and once adjusted, the architecture is configured in quantum light mode whereby single photon detectors (e.g., avalanche photodiodes, photon number resolving detectors, superconducting nanowire detectors) are implemented as the detectors 625 to detect quantum light (e.g., single photons) outputted by the quantum GMZI architecture 600. In some embodiments, once the plurality of phase shifters 615 are zeroed out using bright, light, the quantum GMZI architecture 600 is operated in nonclassical quantum light mode, in which single photons or entangled photon groups are propagated through the quantum GMZI architecture 600, and the plurality of phase shifters implement zero to % phase shifters on the superposition of the single photon in the arms of the quantum GMZI architecture 600 to modify probabilities of the quantum light exiting from one or more of the output ports (e.g., right side ports) of the second Hadamard network 620.

[0049] In some embodiments, the waveguides of the plurality of arms in the quantum GMZI architecture 600 are designed and fabricated to minimize loss as the respective arms propagate classical or quantum light in the quantum GMZI architecture 600. For example, the waveguides are configured in a fan-in configuration 605 to couple light from multiple larger separate light sources into the smaller input interface of the first Hadamard network 610. Further, the waveguides may be configured in a fan-out architecture 613 to connect the waveguides to the plurality of phase shifters 615 without incurring significant optical loss which can affect quantum light processing (e.g., cause decoherence). Further, the waveguides may be configured in a fan-in architecture 617 into the second Hadamard network 620 and / or a fan-out configuration 618 to couple to additional devices, such as other switches, further waveguide routing, fiber interfaces, or light detectors (e.g., photodetectors, photodiodes, or the detectors 625).

[0050] FIG. 7 shows a GMZI switch architecture 700, in accordance with some embodiments. As illustrated, light is input into a first Hadamard network 705 (e.g., a first. Hadamard gate) and phase shifted by the waveguide arm phase shifters 710. In some embodiments, each phase shifter may be implemented by active optical components built by optical waveguides, such as an electro-optical phase shifter comprising an optical waveguide that is combined with electro-optical materials and electrodes. The optical waveguide of the phase shifter may be fabricated from different materials, including silicon, silicon nitride, doped SiO2, a complex oxide (e.g., lithium niobate, barium titanate), or III-V materials.

[0051] In some embodiments, the phase shifter operates by applying an electrical signal to the electro-optical material to change its index of refraction and thereby shift the phase of the light propagating in the waveguide. In some embodiments, the application of the electrical signal to the electro-optical material causes a phase shift from plasma dispersion effects in silicon and III-V semiconductors. In some embodiments, the electrical signaling is applied to control a Pockels effect in the shifter (e.g., as in Lithium Niobate and Barium Titanate, BTO), or cause Kerr effects. In some embodiments, the active material is resistive and thermal-optical effects cause phase shifts in the propagating light.

[0052] In some embodiments, the electrical signaling is applied via electrodes in the phase shifter, where electrodes include different conductive contacts and conductive traces (e.g., metals such as Cu, Al, and / or Au).

[0053] In some embodiments, the pitch of the phase-shifter array is increased by fanning out optical waveguides between the Hadaniard network gates and the plurality of phase shifters thereby reducing undesired crosscouplings between the separate phase shifters (e.g., minimize thermal or piezo-electric couplings). In some embodiments, the phase shifters are implemented as fast phase shifters and slow phase shifters (e.g., heaters or MEMS switches configured as a phase shifter).

[0054] Continuing with reference to FIG. 7, after shifting by the waveguide arm phase shifters 710, the light is then further processed by a second Hadamard network (e.g., the second Hadamard network 725) and output from a plurality of output ports (e.g., to further switches or detectors). In some embodiments, the components of the quantum GMZI switch architecture 700 are fabricated in a single photonic integrated circuit (e.g., on a single substrate) and the components are interconnected using integrated waveguides (e.g., silicon waveguides, silicon nitride waveguides).

[0055] Switching operations may be performed by the GMZI switch architecture 700 as follows. In some embodiments, light (e.g., one or more photons) is inputted into any of the N-input ports (e.g., left side ports of the first Hadamard network 705) and are switched to any of the N-output ports (e.g., right side of the second Hadamard network 725). As discussed, the switching operations may be implemented by the waveguide arm phase shifters 710 including the fast phase shifters 715 and the slow7 phase shifters 720. In some embodiments, the slow phase shifters 720 are driven by a control system (e.g., CPU based system, GPU system, microcontroller, electrical logic circuits). In some embodiments, the control system comprises a plurality of control subsystems comprising a thermal controller 730, an electrical controller 735, and an optical controller 740. In some embodiments, the optical controller 740 receives herald data 775 (e.g., data heralding the arrival of a single photon at a photon-number-resolving detector) and adjusts operation of the quantum GMZI switch architecture 700 based on the received herald data 775. .Although the thermal controller 730, the electrical controller 735, and the optical controller 740 are illustrated as external to the quantum GMZI for explanation and clarity purposes, it is appreciated that components of the thermal controller 730, the electrical controller 735, and the optical controller 740 - such as sensors, waveguides and electrical traces --- may be integrated throughout the GMZI to detect and control different components.

[0056] At a high level, and in accordance with some embodiments, the electrical controller 735 controls the slow phase shifters 720 (e.g., sets biases) to tune and zero out the architecture, and the electrical controller 735 controls the fast phase shifters 715 to finish switching operations (e.g., 0 to w phase shifts to implement transform matrices or dynamic updates for error correction). In some example embodiments, the electrical controller 735 receives herald data 775 from a plurality of single photon sources (e.g., pair source generators) where the signal photon is detected and the idler photon is further propagated to the quantum GMZI switch architecture 700. In some example embodiments, in response to receiving electrical herald data 775 that a photon is being input, on one of the arms of quantum GMZI switch architecture 700, the electrical controller 735 retrieves phase shifter data from a memory (e.g., a look up table having phase shifter settings determined from the transfer matrices) and applies the phase shifter settings to the fast phase shifters 715 at runtime (e.g., during routing of photons for processing of quantum information tasks). As used here, the fast phase shifters 715 generally function as the switching phase shifters that can complete phase shifts more quickly than the slow phase shifters 720 (e.g., heaters). In some example embodiments, both the sets of phase shifters are fast phase shifters that have approximately same shifting speed, wherein one of the phase shifters is used for trimming (e.g., setting phase from 0 to 2k) and the other of the phase shifter on the same arm is used for high speed switching during operation (e.g., for single photon muxing).

[0057] In some embodiments, during operation, the performance of the fast phase shifters 715 and / or the slow phase shifters 720 may drift or degrade with time. The optical controller 740 may be configured to detect the optical signal (e.g., from bright light or single photon detectors, detecting a herald photon via the herald detector) and provide feedback to the electrical controller 735. The electrical controller 735 may then adjust the phase shifter driving signals in the control circuits and the drivers to configure (e.g., bias) the phase shifters to compensate for the drifts or performance degradation.

[0058] In some embodiments, the phase shifters are sensitive to local temperature gradient of the environment in which the quantum GMZI switch architecture 700 operates. In some embodiments, throughout the operation, the temperature sensors in the thermal controller 730 monitor the temperatures at different locations of the quantum GMZI switch architecture 700 (e.g., the local temperatures of each phase shifter in the waveguide arm phase shifters 710 or the local temperatures of the first Hadamard network 705 and the second Hadamard network 725). The temperature sensors provide the feedback to the control circuits in the electrical controller 735. If the local temperature needs to be adjusted, the control circuits of the electrical controller 735 comprise logic or instructions to send signals to the heaters in the thermal controller 730 to cause the heaters to heat up the GMZI locally.

[0059] In some embodiments, the electrical controller 735 is implemented by electronic integrated circuits comprising logic to implement controls. The integrated circuits may include analog circuits and digital circuits such as high-speed phase shifter drivers, biasing network circuits, monitoring and control circuits. The electronic integrated circuits may be manufactured by different platforms, such as CMOS, SiGe, or HI-V. In some embodiments, large output extinction ratio are enabled via precise control over phase-shifts in each arm. In some embodiments, the precise control is implemented via programmable DACs that control voltage levels for the slow and fast phase shifters, as well as feedback control for thermal regulation. In some embodiments, schemes such as pre-emphasis and close electrical proximity of driver circuits are implemented by the electrical controller 735 to perform optimization and achieve precise voltage settings for the settings of the fast, phase shifters 715.

[0060] In some embodiments, the optical controller 740 comprises optical waveguide devices, photodetectors (e.g., bright light photodetectors, monitor photodiodes, single photon detectors), and tapping components (e.g., optical taps or switches configured to activate and tap light from a given waveguide). In some embodiments, the bright-light photodetectors of the optical controller 740 are formed from materials including one or more of: doped silicon, germanium, or superconducting materials. In some embodiments, upon the optical signal being detected by one or more of the photodetectors, electrical signal is then generated from the optical signal and transmitted to the electrical controller 735 for control signal processing.

[0061] In some embodiments, the thermal controller 730 comprises a plurality of temperature sensors that detect temperature. For example, the temperature sensors (e.g., thermometers) can be implemented by sensing the electrical signals of different materials, such as DLTM (e.g., doped Si), metals (e.g., Al, Cu, W, TiN, etc.), and dielectric materials (e.g., Barium Titanate). When temperature changes, the monitoring and control circuits sense the change of the electric signal (e.g., I-V) of the temperature sensors, and obtain the (local) temperature readings. In some embodiments, the temperature sensors are implemented by the optical signals of different materials, such as Si, SiN, Complex Oxide (e.g., Lithium Niobate, Barium Titanate), or III-V. In an optical resonator implementation, the resonant wavelength is a function of the temperature due to the thermo-optical effect of the materials. In these embodiments, the heater element is formed from materials having resistance, such as doped Si, metals (e.g., Al, Cu, W, TiN, etc.), and / or doped dielectrics.

[0062] In some embodiments, each arm in the GMZI switch architecture 700 is controlled by a set of phase shifters: a slow phase shifter 720 and a fast phase shifter 715. At a high level, the slow phase shifter 720 is configured to minimize or zero out a phase difference between input and output light. For example, input light is light inputted into the left side of the first Hadamard network 705 and the output light is light outputted from the right side of the second Hadamard network 725 (e.g., the second Hadamard waveguide coupler network) and measured to perform adjustments. In some embodiments, the slow phase shifters 720 are implemented to configure the quantum GMZI switch architecture 700 for a given optical processing configuration (e.g., zero out fabrication-based loss sources, adjust global phases, or compensate for temperature variations across the optical device). For example, the slow phase shifter 720 is configured to manage local temperature issues, such as the differences between the temperature of different areas of the quantum GMZI switch architecture 700 to ensure the phase differences are zeroed out. Further, in accordance with some embodiments, the slow phase shifters 720 are implemented to zero out phase difference between different GMZIs (e.g., other instances of the quantum GMZI switch architecture 700 that are connected to the GMZI shown in FIG. 7), such that multiple GMZIs are interconnected and zeroed out across all devices to ensure the fast phase shifters operate with sufficient 0 to phase shifts in operation.

[0063] In some embodiments, one or more of the fast phase shifters 715 are implemented during operation of the GMZI switch architecture 700 to provide precise 0 to phase shift swings to implement quantum entanglement operations (e.g., apply a desired Hadamard transformation matrix) and to provide routing operations (e.g., routing of bright light, routing of single photons, routing of entangled state photon probability distributions). Although, in FIG. 7, the waveguides are illustrated is straight, it is appreciated that the waveguides may fan-in and fan-out as discussed below with reference to FIG. 9 and FIG. 10.

[0064] In some example embodiments, the slow phase shifters 720 are not implemented. In place of the slow phase shifters 720, the DC bias voltages of the fast phase shifters 715 may be modified to adjust the static arm phase offsets for a given fast phase shifter 715. It will be appreciated that the electro-optical material 1118, when activated by the electrical stimulus, undergoes a change in refractive index to couple a mode of the light within the waveguide into a portion of the electro-optical material 1118, thereby applying a phase shift to the light,

[0065] FIG. 8 shows close-up view's of example components of a PIC based GMZI, in accordance with some example embodiments. The example components can be arranged in networks to implement the interference networks (e.g., Hadamard networks). The crossing coupler 800 (e.g., star coupler, low-loss MMI) comprises two waveguides that cross one another to create a 2x2 coupler arrangement. The direction coupler 805 comprises two waveguides that come near to one another to evanescently couple light between the waveguides to form a 2x2 coupler. The direction coupler 805 can be implemented as a 50:50 coupler (e.g., beam splitter), 0:100 coupler, or 100:0 coupler, in accordance with different implementations.

[0066] FIG. 9 shows a quantum GMZI architecture 900 in a balanced configuration in which the optical powers across the network are equivalent in accordance with some embodiments. The example quantum GMZI architecture 900 comprises two instances of an 8x8 Hadamard network: a first Hadamard network 910 and a second Hadamard network 920, which are each implemented using the configuration illustrated in FIG. 10 (flipped, in the case of second Hadamard network 920).

[0067] In some embodiments, such as in FIG. 9, the GMZI is designed so that the optical paths are balanced by default (e.g., the first Hadamard network 910 is a mirror image of the second Hadamard network 920) which may improve scalability of the GMZI by creating large self-similar waveguide network (e.g., Fractal networks) that are balanced and remain in phase. In some embodiments, light is input into a plurality of couplers 905 (e.g., grating couplers) and is coupled to a plurality of couplers 925 (e.g., a plurality of grating couplers). On a high level, the quantum GMZI architecture 900 comprises the first Hadamard network 910 and the second Hadamard network 920 connected by phase shifters 915 (e.g., single phase shifters, segmented phase shifters).

[0068] FIG. 10 show's the first Hadamard network 910 in accordance with some embodiments. In the illustrated example of FIG. 10, the light is inputted into a plurality of directional couplers 1005 configured as 50:50 power splitters. A plurality of directional couplers 1005 are coupled into a crossing network 1010 comprising a plurality of interconnected star couplers (e.g., a waveguide star crossing network). As illustrated, one or more of the star networks in the crossing network 1010 have pairs of unused ports that are terminated with waveguide absorbers (not depicted), in accordance with some embodiments. The crossing network 1010 is physically expanded via an array of bends 1013 (e.g., Euler bends of fan-out or fan-in waveguide arrangements) that are coupled via a further array of bends 1017 into splitters 1015 (e.g., a plurality of directional couplers) configured as 50:50 power splitters, which are then coupled into a larger crossing network 1020 of star couplers, wherein one or more of the star couplers along the edge have unterminated ports and the star couplers in the middle of the crossing network 1020 have all ports that, are all connected to other or subcomponents (e.g., directional couplers). Further, the directional couplers 1025 are configured as 50:50 power splitters, which couple light to the phase shifters 915.

[0069] As described above, in some configurations, components of the photonic integrated circuits can impart unintended phase changes that accumulate and cause inaccuracies in phase shift operations of an GMZI. Accordingly, in some example embodiments, segmented phase shifters may be used on the waveguide arms to negate these unwanted phase changes.

[0070] FIG. 11 show?s an example segmented phase shifter 1100 in accordance with some embodiments. The segmented phase shifter 1100 includes a sequence of phase shifter segments along a section of a waveguide arm 1112, shown in FIG. 11 as a first phase shifter segment 1102, second phase shifter segment 1104, third phase shifter segment 1106, fourth phase shifter segment 1108, and four coarse phase shifter segments 1110. In some example embodiments, the waveguide arm 1112 comprises an electro-optical material that receives stimulus (e.g., voltage) from electrodes to effectuate a change to the phase of the light propagating in the waveguide arm 1112, as discussed above with reference to FIG. 7 (e.g., III-V materials, complex oxides such as lithium niobate or barium titanate). [0071 ] In some example embodiments, the phase shifter segments are configured to effect a range of phase shifts (also called phase adjustments) from 0 to 2x radians, or close to 2ir radians. For example, the segmented phase shifter 1100 shown in FIG. 11 may be configured such that each phase shifter segment effects a magnitude of phase shift as shown in Table 1 below: Segment first second third fourth coarse coarse coarse coarse (1102) (1104) (1106) (1108) (1110) (1110) (1110) (1110) Phase shift 2x / 80 2k / 40 2x / 20 2x / 10 2x / 5 2x / 5 2x / 5 2x / 5 Table 1

[0072] Thus, the segmented phase shifter 1100 configured according to Table 1 is capable of applying phase shifts across the range from 0 to (2%)x(79 / 80) radians, to a degree of precision within (2tt / 80) / 2 radians. The configuration of phase shifter segments shown in Table 1 may also exhibit phase shifting accuracy that is robust against errors (e.g., 20% error or more, based on design simulation) introduced by fabrication variability or other sources of segment length variation. For example, in some embodiments the segment lengths may be rescaled to cover a range of greater than 2x -- the configuration shown in Table 1 may exhibit a high degree of phase shifting accuracy (e.g., within 1%, based on design simulation) even after such rescaling.

[0073] Each segment of the segmented phase shifter 1100 includes a length of electro-optical material 1118 (e.g., barium titanate layered on top of a silicon nitride waveguide) in contact with the waveguide arm 1112, a waveguide electrode 1114 driving the electro-optical material 1118, and an electrode interface 1116 for providing an electrical stimulus to the waveguide electrode 1114 to apply the segment's respective phase shift to the waveguide arm 1112 via the electro-optical material 1118, The electrical stimulus applied by the electrode interface 1116 via the waveguide electrode 1114 may be a binary stimulus, such that each segment switches between an active state (in which its respective phase shift is applied to the waveguide arm 1112 and the light propagating within) and an inactive state (in which the particular segment does not apply a phase shift to the waveguide arm 1112). The electrode interface 1116 may provide a circuit interface to a control board or other circuit component for selectively providing distinct electrical stimuli to the segments of the array of phase shifters of the GMZI. An example control board layout for an alternative configuration of a segmented phase shifter is described below with reference to FIG. 12.

[0074] In some example embodiments, the segments may each have a respective length that is proportional to the magnitude of the segment's respective phase shift. For example, in an implementation of the segmented phase shifter 1100 applying a maximum electrical stimulus of 3 V (corresponding to activation of all eight segments) and spanning a length of the waveguide arm 1112 that is approximately 4 mm in length, the electro-optical material 1118 of the segments may have respective lengths of 50 pm for first phase shifter segment 1102, 100 pm for second phase shifter segment 1104, 200 pm for third phase shifter segment 1106, 400 pm for fourth phase shifter segment 1108, and 800 pm for each coarse phase shifter segment 1110. Thus, in some examples, the respective phase adjustment applied by each phase shifter segment of the segmented phase shifter 1100 when activated is proportional to a length of the phase shifter segment along the waveguide arm 1112.

[0075] The segmented phase shifter 1100 may address one or more technical problems presented by GMZIs, optical switches, and other optical devices. In some example embodiments, the segmented phase shifter 1100 can be used to replace the slow phase shifters 720 and fast phase shifters 715 of GMZI switch architecture 700. In contrast to the slow phase shifters 720, which may be implemented as relatively slow, thermally-timed analog phase shifters, the segmented phase shifter I100 can perform relatively fast, realtime switching by selectively activating and deactivating subsets of segments. This may enable the segmented phase shifter 1100 to perform the real-time phase-shifting of the fast phase shifters 715 (e.g., fast 180 degree or 7r-radian phase switching), allowing the fast phase shifters 715 to be replaced by segmented phase shifters 1100. Also, because the segmented phase shifter 1100 can apply phase shifts over a full or nearly full range of 0 to 2te radians (360 degrees), it can be used to compensate for phase errors on each waveguide arm 1112 detected during a calibration stage, thereby replacing the slow phase shifters 720. In addition, whereas the slow phase shifters 720 of GMZI switch architecture 700 are capable of compensating for routing phase errors, they are not typically able to compensate for accumulated phase error that is internal to the couplers (e.g., crossing couplers 800 or direction couplers 805 ) of the Hadamard network itself, such as phase error caused by process variations of the components, surface roughness, or decreased phase accuracy caused by the direction couplers (e.g., direction couplers 805). In contrast, the segmented phase shifter 1100 may be able to compensate for these additional sources of phase error. In some example embodiments, the segmented phase shifter 1100 may also be configured to detect and correct for phase errors that change during operation.

[0076] In some example embodiments, such as the segmented phase shifter 1100 shown in FIG. 11, the coarse phase shifter segments 1110 have two electrode interfaces 1116 rather than one electrode interface 1116 for the shorter segments. In some examples, the waveguide electrode 1114 of a given segment may be formed as a bump electrode having one or more bumps. For example, the waveguide electrode 1114 for each coarse phase shifter segment 1110 may operate in a manner analogous to a bumped capacitor, with the voltage of the electrical stimulus being divided between the two electrode interfaces 1116 and applied to the electro-optical material 1118 via two bumps. In various example embodiments, the number of bumps and / or electrode interfaces 1116 used per segment may be varied in accordance with segment length, but in some cases, design considerations (e.g., the spatial density of the bumping interface, the speed of operation, and so on) may result in different distribution of bumps and / or electrode interfaces 1116 for various segments. These design considerations may be informed by electrical modelling. Electrically, the phase shifter segments can be designed to behave either as travelling wave phase shifters, impedance-matched structures, or as lumped elements. In some cases, there may be a benefit to keeping the lengths of the phase shifter segments short relative to a wavelength of the electrical signal used to stimulate the segments, such that the (a / 16) rule is satisfied.

[0077] In some embodiments, a segmented phase shifter may use a different configuration from the illustrated example segmented phase shifter 1100 shown in FIG. 11. Some example embodiments may vary the amount of phase shift applied by different segments by configuring the segments to receive and apply differing magnitudes of electrical stimulus (e.g., voltage) instead of, or in addition to, the segments having differing lengths along the waveguide arm 1112. For example, some embodiments could include eight equal-length segments applying the same respective phase shifts shown in Table 1 above, wherein each segment is configured to apply a respective voltage value proportional to its corresponding phase shift amount as shown in Table 1. In some example embodiments, a segmented phase shifter may include more or fewer segments than the eight segments of the example segmented phase shifter 1100, and / or segments having a distribution of phase shift amounts that differ from the distributions shown in Table 1.

[0078] A second example embodiment of a segmented phase shifter is described below with reference to FIG. 12 and FIG. 13.

[0079] FIG. 12 shows a GMZI layout 1200 incorporating an array 1208 of segmented phase shifters 1206 according to a second example embodiment, described below with reference to FIG. 13, that differs from the segmented phase shifter 1100 of FIG. 11. The GMZI layout 1200 includes a. first Hadamard network 1202 (which may be implemented according to examples described herein), a second Hadamard network 1204 (which may be implemented according to examples described herein), and the array 1208 of segmented phase shifters 1206, laid out on a surface of a control board 1210. The waveguide arms can be seen crossing and splitting through the first Hadamard network 1202, passing through the segmented phase shifters 1206 in the array 1208, and then continuing to the second Hadamard network 1204 for recombination.

[0080] The control board 1210 includes circuit logic, such as electrical and / or photonic circuit logic, for controlling the array 1208 of segmented phase shifters 1206, and / or for performing one or more of the methods described herein. In some examples, the control board 1210 includes a memory, such as an array of registers, for storing information. In some examples, the control board 1210 includes at least one controller, which may include an electrical controller 735, a thermal controller 730, and / or one or more hardware processors for processing machine-executable instructions stored in the memory to perform one or more of the methods described herein, including computing segment activation patterns, performing calibration of the array 1208 of segmented phase shifters 1206, and operating components of the GMZI system including light emitters, photodetectors, and so on. In some examples, the memory, one or more of the controllers, and / or one or more of the detectors may be located off-board as part of a separate component in communication with the control board 1210. In some examples, the GMZI, the memory, the at least one controller, and the one or more detectors may be regarded as components of a single system that operate together to perform one or more of the methods described herein. [0081 ] In some examples, the segmented phase shifters 1206 are all controlled electrically by the electrical controller 735, such that the system does not need to include a thermal controller 730.

[0082] FIG. 13 shows a detailed view of one of the segmented phase shifters 1206 of the GMZI layout 1200 of FIG. 12. The segmented phase shifter 1206 includes five phase shifter segments of equal length, in contrast to the eight-segment configuration of the segmented phase shifter 1100. In some examples, the five-segment configuration of the segmented phase shifter 1206 is operable to apply an equal amount of phase shift for each segment that is activated: for example, each of the five phase shifter segments 1302, when activated, applies 20% of the maximum phase adjustment capable of being applied by the segmented phase shifter 1206, such as a phase adjustment of 2k / 5 for a segmented phase shifter 1206 configured to apply 0 to 2k radians of phase adjustment. In some examples, each phase shifter segment 1302 applies a phase adjustment with a magnitude determined by the magnitude of an electrical stimulus applied by the control board 1210 to the phase shifter segment 1302, such as a voltage set by the control board 1210 and maintained between the electrode interfaces 1306 and waveguide electrodes 1304 to the electro-optical material 1310 on the waveguide arm 1308 when the phase shifter segment 1302 is activated.

[0083] Thus, in some examples, the respective phase adjustment applied by each phase shifter segment of the segmented phase shifter 1206 when activated is proportional to, or otherwise based on, a voltage applied to the phase shifter segment to activate the phase shifter segment.

[0084] As used herein, the term “stimulus” or “electrical stimulus” refers to a deviation from a baseline state, such as an increase or a decrease in voltage from a baseline voltage or other baseline electrical signal. The baseline voltage may be zero voltage or a non-zero voltage.

[0085] FIG. 14 show's a flow diagram of a method for processing light using a GMZI, in accordance with some example embodiments. Although the example method 1400 depicts a particular sequence of operations, the sequence may be altered without departing from the scope of the present disclosure. For example, some of the operations depicted may be performed in parallel or in a different sequence that does not materially affect the function of the method 1400. In other examples, different components of an example device or system that implements the method 1400 may perform functions at substantially the same time or in a specific sequence.

[0086] Although the method 1400 is described with reference to the components of various example GMZIs described herein, it will be appreciated that the operations of the method 1400 may be performed by any of a number of different GMZI configurations.

[0087] Method 1400 is performed at the operation stage, as described above.

[0088] According to some examples, the method 1400 includes receiving light at operation 1401. As described above, the light may be quantum light or bright light. It is received by a first coupler network (e.g., first Hadamard network) of the GMZI.

[0089] According to some examples, the method 1400 includes distributing the light by the first Hadamard network at operation 1402. The first Hadamard network distributes the light to one or more of the plurality of waveguide arms (e.g., an array of waveguide arms).

[0090] According to some examples, the method 1400 includes adjusting a phase portion of the light at operation 1403. Each phase shifter in the array of phase shifters is operable to adjust the phase of the light in its respective waveguide arm. Embodiments using segmented phase shifters may perform the phase adjustment of the light according to further methods described below with reference to FIG. 17 and / or FIG. 18, after calibration according to a further method described with reference to FIG. 16.

[0091] According to some examples, the method 1400 includes combining the light by a second coupler network (e.g., second Hadamard network) of the GMZI at operation 1404. The second Hadamard network combines the light from one or more of the plurality of waveguide arms of the array, thereby generating combined light.

[0092] According to some examples, the method 1400 includes outputting the combined light from one or more output ports of the GMZI at operation 1405. The combined light is propagated from the second Hadamard network to the one or more output ports, and the output ports output the combined light. In some examples, the combined light includes multiple distinct beams or portions of light, each of which is output by a distinct output port.

[0093] FIG. 15 shows a flow diagram of a method for processing quantum light using a GMZI, in accordance with some example embodiments. Although the example method 1500 depicts a particular sequence of operations, the sequence may be altered without departing from the scope of the present disclosure. For example, some of the operations depicted may be performed in parallel or in a different sequence that does not materially affect the function of the method 1500. In other examples, different components of an example device or system that implements the method 1500 may perform functions at substantially the same time or in a specific sequence.

[0094] Although the method 1500 is described with reference to the components of various example GMZIs described herein, it wall be appreciated that the operations of the method 1500 may be performed by any of a number of different GMZI configurations.

[0095] Method 1500 is performed at the operation stage, as described above. Method 1500 may be regarded as a special case of method 1400, in which the GMZI operates on a superposition of quantum tight in a nonclassical quantum light mode, as described above.

[0096] According to some examples, the method 1500 includes receiving quantum tight at operation 1501. The quantum light is received by the first Hadamard network of the GMZI.

[0097] According to some examples, the method 1500 includes splitting the quantum tight at operation 1502. The quantum light is split by the first Hadamard network into one or more of the waveguide arms.

[0098] According to some examples, the method 1500 includes interfering the quantum light at operation 1503. As described above with reference to FIG. 5 and FIG. 6, in some examples, the quantum light may be split into two waveguide arms and can be interfered with 50% of the light transmitted to a given output port via the second Hadamard network, which combines the quantum light. For example, the array of phase shifters may implement zero phase adjustments and ir phase adjustments on the superposition of the quantum light in the waveguide arms to modify probabilities of the quantum tight exiting from one or more of the output ports.

[0099] According to some examples, the method 1500 includes outputting the quantum light at operation 1504. The quantum light is output by one or more output ports of the GMZI. In some examples, the quantum light output by a given output port may be output to a detector, such as a single-photon detector, for measurement.

[0100] Whereas method 1400 and method 1500 are generally applicable to GMZI examples described herein, a further set of methods are described with reference to FIG, 16, FIG. 17, and FIG. 18 that can be performed by a system including a GMZI having segmented phase shifters.

[0101] FIG. 16 illustrates an example method 1600 for calibrating an array of segmented phase shifters of a GMZI. Although the example method 1600 depicts a particular sequence of operations, the sequence may be altered without departing from the scope of the present disclosure. For example, some of the operations depicted may be performed in parallel or in a different sequence that does not materially affect the function of the method 1600. In other examples, different components of an example device or system that implements the method 1600 may perform functions at substantially the same time or in a specific sequence.

[0102] Method 1600 performs calibration of the GMZI during the calibration stage, prior to the operation stage or in between iterations of the operation stage.

[0103] According to some examples, the method 1600 includes propagating bright light through one or more light paths of the GMZI to generate bright combined light at operation 1602. The light paths of the GMZI are defined by the first coupler network, the waveguide arms, and the second coupler network. For example, light propagating from a first input port, through one or more sequentially arranged crossing couplers 800 and / or direction couplers 805 of the first coupler network, through a single waveguide arm, and then through one or more sequentially arranged crossing couplers 800 and / or direction couplers 805 of the second coupler network to arrive at a given output port may be regarded as following a single light path. In some examples, the light may propagate from a single input port, through multiple light paths (e.g., through multiple waveguide arms), and then be partially or fully recombined before some or all of the light arrives at a given output port.

[0104] According to some examples, the method 1600 includes detecting the bright combined light to determine a phase adjustment pattern effective to compensate for the respective phase error for each of the one or more light paths at operation 1604. Detectors may be configured to receive the bright combined light output by the output ports and measure the transmitted power of the bright combined light at each output port. The phase adjustment applied by each segmented phase shifter in the array of segmented phase shifters can then be individually adjusted to optimize the transmitted power of the combined bright light at the output port under test. The resulting pattern of phase shifter settings may be referred to herein as an optimal phase adjustment pattern for that input port, where each input port can have a corresponding stored optimal phase adjustment pattern. The optimal phase adjustment pattern may include a respective pattern of segment activations for each segmented phase shifter in the array, or for only one or more segmented phase shifters in the array. The optimal phase adjustment pattern implicitly accounts for phase error introduced along the light path(s) being calibrated, by applying a pattern of phase adjustments that optimize transmitted power and therefore correct for phase errors, which would reduce the transmitted power if present and uncorrected.

[0105] In some examples, the pattern of bright light inputs provided to the first coupler network at a given time during the calibration stage is configured such that the bright combined fight output by a given output port corresponds to a single light path, allowing the detectors to measure the transmitted power of the light at a given output port at a given time during the calibration stage in order to generate an optimal phase adjustment pattern for the corresponding light path. The at least one controller of the system controlling the GMZI may be configured to apply a time-varying pattern of bright light to the inputs of the GMZI in order to measure a transmitted power of each light path independently.

[0106] According to some examples, the method includes storing one or more of the generated optimal phase adjustment patterns at operation 1606. The at least one controller, after generating an optimal phase adjustment pattern for light propagating from a given input port, through the one or more light paths, to a given output port at operation 1604, may generate and store data encoding the optimal phase adjustment pattern for the array of phase shifters in the memory. Operations 1602 through operation 1606 may be repeated for each mapping of a given input port to a given output port, with each phase shifter being calibrated for each such mapping. The combination of all such calibration settings for a given mapping of input port to output port may constitute a single optimal phase adjustment pattern.

[0107] In some examples, as described above, the memory may include a look up table of phase shifter values used for controlling the phase shifters; in some examples, the memory may also include a look up table of optimal phase adjustment patterns for each light path, which is retrieved and used during the operation stage, as described below with reference to FIG. 17 and FIG. 18. In this way, the data stored in the look up tables or otherwise stored in the memory may be used not only for controlling the segmented phase shifters to perform runtime phase switching operations (e.g., 0 to % phase switching, or other target phase value, such as 0 to u / 4 based switching), but also to perform error correction to compensate for accumulated phase error on the various light paths of the GMZI.

[0108] Thus, in some examples, a system for operating a GMZI includes at least one controller and a memory. The at least one controller is configured to perform calibration during a calibration stage, prior to receiving the light by the first coupler network during the operation stage. Bright light is propagated through one or more light paths of the GMZI defined by the first coupler network, the waveguide arms, and the second coupler network to generate bright combined light. The bright combined light is detected to determine a respective optimal phase adjustment pattern for each of the one or more light paths. The optimal phase adjustment pattern is stored in the memory for each light path, the optimal phase adjustment pattern being representative of an error correction phase adjustment effective to negate a respective phase error of the light path.

[0109] FIG. 17 illustrates an example method 1700 for adjusting the phase of light in a waveguide arm of the GMZI using a segmented phase shifter. Although the example method 1700 depicts a particular sequence of operations, the sequence may be altered without departing from the scope of the present disclosure. For example, some of the operations depicted may be performed in parallel or in a different sequence that does not materially affect the function of the method 1700. In other examples, different components of an example device or system that implements the method 1700 may perform functions at substantially the same time or in a specific sequence.

[0110] Method 1700 processes the light during the operation stage, after the calibration stage. Method 1700 may be regarded as a specific implementation of operation 1403 of method 1400, for a single segmented phase shifter applying phase adjustment to a single waveguide arm. Thus, operation 1403 may be regarded as performing method 1700 for each segmented phase shifter being used to process the light of method 1400.

[0111] According to some examples, the method 1700 includes retrieving the optimal phase adjustment pattern at operation 1702. For example, as described above, the optimal phase adjustment pattern may correspond to a mapping of an input port to an output port, wherein the light propagates from the input port to the output port via one or more light paths including a first light path that includes a first waveguide arm coupled to a first segmented phase shifter. The optimal phase adjustment, pattern encodes calibration settings for one or more of the phase shifters coupled to the one or more light paths. The optimal phase adjustment pattern may be retrieved by a controller from a look up table in the memory.

[0112] According to some examples, the method 1700 includes generating a segment activation pattern based on the optimal phase adjustment pattern at operation 1704. The segment activation pattern is a pattern of phase shifter segments of a first segmented phase shifter, coupled to the first waveguide arm, which are to be activated in order to apply a phase adjustment to the light in the first waveguide arm that is effective to negate or otherwise compensate for the phase error of the first light path. Thus, for example, if the optimal phase adjustment pattern for the first light path implicitly or explicitly encodes a phase error value of -13^ / 80 radians for the first light path, the controller may generate a segment activation pattern that, activates one or more phase shifter segments of the first segmented phase shifter that collectively apply +1371. / 80 radians of phase adjustment, or as close as possible to +13^ / 80 radians of phase adjustment, when activated. In the case of the example segmented phase shifter 1100 having phase adjustment values as shown in Table 1 above, this could mean a phase adjustment of + 12te / 80 radians by activating the second phase shifter segment 1104 (to apply +4k / 80 radians) and third phase shifter segment. 1106 (to apply +8ti / 80 radians). Alternatively, the segmented phase shifter 1100 could apply a phase adjustment of +14W80 radians by activating the first phase shifter segment 1102 (to apply +2tt / 80 radians), the second phase shifter segment 1104 (to apply +4% / 80 radians), and the third phase shifter segment 1106 (to apply +8% / 80 radians). These alternatives correspond to two alternative segment activation patterns, both based on an optimal phase adjustment pattern for the first light path encoding a phase error value of -13re / 80 radians.

[0113] According to some examples, the method includes activating the one or more phase shifter segments according to the segment activation pattern to compensate for the phase error of the first light path at operation 1706. In some examples, the at least one controller is configured to apply electrical stimuli to the phase shifter segments of the first segmented phase shifter according to the segment activation pattern. For example, the first example segment activation pattern described above could be applied to the segmented phase shifter 1100 as a voltage stimulus applied between the pair of electrode interfaces 1116 of the second phase shifter segment I104 and a voltage stimulus applied between the pair of electrode interfaces 1116 of the third phase shifter segment 1106, with no voltage stimulus applied between the pairs of electrode interfaces 1116 of the first phase shifter segment 1102, fourth phase shifter segment 1108, or any of the coarse phase shifter segments 1110.

[0114] Thus, in some examples, a system for operating a GMZI includes at least one controller and a memory. The at least one controller is configured to process light during an operation stage following the calibration stage. During the operation stage, the at least one controller retrieves, from the memory, the optimal phase adjustment pattern corresponding to an output port of interest. The segment activation pattern is generated based on the optimal phase adjustment pattern. The one or more phase shifter segments are activated according to the segment activation pattern to compensate for the phase error of the first light path. In some examples, each phase shifter segment is configured to receive a respective electrical stimulus to activate the phase shifter segment.

[0115] In some examples, two or more phase shifter segments of the first segmented phase shifter each apply a same phase adjustment when activated. Examples include the five 20%-maximum phase shift phase shifter segments 1302 of the example segmented phase shifter 1206, or the four coarse phase shifter segments 1110 of the segmented phase shifter 1100.

[0116] In some examples, two or more phase shifter segments of the first segmented phase shifter each apply different phase adjustments from each other when activated. Examples include the first phase shifter segment 1102 through fourth phase shifter segment 1108 of the coarse phase shifter segment 1110.

[0117] In some examples, the plurality of phase shifter segments are operable, when each phase shifter segment is activated, to collectively apply a maximum phase adjustment to the light in the first, waveguide arm, the maximum phase adjustment being substantially equal to 2w radians. For example, the coarse phase shifter segment 1110 described above with reference to Table I has a maximum phase adjustment within te / 40 radians of radians.

[0118] In some examples, the plurality of phase shifter segments are operable, when each phase shifter segment is deactivated, to collectively apply zero phase adjustment to the light in the first waveguide arm. The plurality of phase shifter segments are operable to collectively apply any of a set of collective phase adjustments to the light in the first waveguide arm, each collective phase adjustment corresponding to a respective segment activation pattern, the set of collective phase adjustments ranging from zero phase adjustment to the maximum phase adjustment (e.g., approximately 2% radians), each phase adjustment of the set of phase adjustments being within w / 80 radians of each adjacent phase adjustment of the set of phase adjustments. Thus, the plurality of phase shifter segments may be operable to apply phase adjustment with an accuracy or resolution of within ti / 80 radians.

[0119] In some examples, method 1700 may be performed independently for multiple segmented phase shifters of the array of phase shifters, for example as part of operation 1403 of method 1400. That is, for example, each arm of a GMZI has a segmented phase shifter, and for each input port, each of the segmented phase shifter’s have lookup table values from calibration to maximize the intensity at one or more output ports. Upon receiving light at the input port at run time, each arm’s phase shifter stored values are used to set each arm’s phase shifter such that the collective result is the target phase shift of light the outputs (e.g., to route the light, or apply a desired transfer matrix).

[0120] In some example embodiments, multiple input ports may receive light for processing in the GMZI. For example, a GMZI may receive light at the first input port and the third input port at the same time. In some example embodiments, one of the input ports is prioritized, such that that prioritize input port’s phase shifter values are what is used to set the phase shifters for each arm. That is, for example, in the look-up table there are phase shifter settings to be applied for when light is input into the first input port (from a first input port calibration sequence; FIG. 16), and there are other different-phase shifter settings to be applied for when light is input into the third input port (e.g., from a third input port calibration sequence; FIG. 16). If in the given scenario light is to be received by the first and third input ports, the first input port may be prioritized and its stored phase shifter values from the look up table are what is used to reach the target phase shift. In some example embodiments, which input ports are to be prioritized over other input ports can be chosen at random, or can be preconfigured before runtime (e.g., based on which input port’s phase paths yield the best results, such as most accurate phase shifts).

[0121] FIG. 18 illustrates an example method 1800 for processing quantum light using a GMZI having segmented phase shifters. Although the example method 1800 depicts a particular sequence of operations, the sequence may be altered without departing from the scope of the present disclosure. For example, some of the operations depicted may be performed in parallel or in a different sequence that does not materially affect the function of the method 1800. In other examples, different components of an example device or system that implements the method 1800 may perform functions at substantially the same time or in a specific sequence.

[0122] Method 1800 is performed at the operation stage, as described above. Method 1800 may be regarded as a special case of method 1500, in which the GMZI operates on a superposition of quantum light in a nonclassical quantum light mode using segmented phase shifters calibrated according to method 1600 and activated (for the purpose of phase error correction) according to method 1700.

[0123] According to some examples, the method 1800 includes receiving and splitting quantum light at operation 1802. Operation 1802 may be regarded as corresponding to operations 1501 and 1502 of method 1500, the quantum light is received by the first coupler network and split into one or more of the waveguide arms of the array of waveguide arms.

[0124] According to some examples, the method 1800 includes retrieving an optimal phase adjustment pattern corresponding to one or more light paths including a first light path and second light path at operation 1804. The first light path passes through a first waveguide arm, and the second light path passes through a. second waveguide arm. The first light path and second light path are two of the light paths through which the quantum light may propagate according to the quantum light input location and the configuration of the first coupler network.

[0125] According to some examples, the method 1800 includes generating a. first segment activation pattern at operation 1806. In some examples, the first segment activation pattern is equivalent to sum of tt radians (or another a target radian value) added to an error correction phase adjustment for the first light path. Operation 1806 corresponds to a runtime phase adjustment of the target radian value to the phase adjustment applied by the first segmented phase shifter coupled to the first waveguide arm. This runtime phase adjustment is used to perform the interference of the quantum light, as in operation 1503, in conjunction with phase adjustment (or lack thereof) applied to other waveguide arms through which the quantum light can propagate. By summing the runtime phase adjustment amount of x radians (or another a target radian value) with the error correction phase adjustment, the controller activates the first segmented phase shifter to simultaneously correct for phase error in the first light path and apply the runtime phase adjustment to perform quantum interference. In some examples, both the runtime phase adjustment and the error correction phase adjustment are implicit in the retrieved optimal phase adjustment pattern: during the calibration stage, patterns of runtime phase adjustments combined with error correction phase adjustments may be generated as part of an optimal phase adjustment pattern, because optimizing the transmitted power at a given output port may require not only phase error correction but also a pattern of runtime phase adjustments for the various light paths.

[0126] In some examples, generating the first segment activation pattern may require a wrap-around summing operation, such that phase adjustments outside of the range of the segmented phase shifter (e.g., below zero or above 2jt radians) are replaced with a functionally equivalent phase adjustment (e.g., -^ / 2 radians is replaced with 3w / 2 radians) by the controller.

[0127] According to some examples, the method 1800 includes activating the first segmented phase shifter according to first segment activation pattern to at least partially compensate for the phase error of the first light path, and to perform the runtime phase adjustment, at operation 1808. As described above with reference to operation 1706 of method 1700, a voltage stimulus may be applied between the electrode interfaces 1116 of the phase shifter segments being activated in order to implement the first segment activation pattern.

[0128] According to some examples, the method 1800 includes generating a second segment activation pattern equivalent to the second error correction phase adjustment at operation 1810. Operation 1810 may be performed in an analogous manner to operation 1806.

[0129] According to some examples, the method 1800 includes activating a second segmented phase shifter coupled to the second waveguide arm according to the second segment activation pattern to compensate for phase error of the second light path at operation 1812. Operation 1812 may be performed in an analogous manner to operation 1808.

[0130] According to some examples, the method 1800 includes detecting combined light propagating through the first light path and second light path at operation 1814. After combining the quantum light in the second coupler network to generate combined quantum light, a first portion of the combined quantum light (which may include one photon or entangled group of photons, or may include zero photons) is propagated to a first output port. A first single-photon detector may be used to measure the combined quantum light at the first output port.

[0131] The following are example embodiments:

[0132] Example lisa method for processing light in an integrated generalized Mach-Zehnder Interferometer (GMZI), the method comprising: receiving, by a first coupler network in the GMZI, light comprising one or more photons; distributing, using the first coupler network, the light to one or more of a plurality of waveguide arms in the GMZI; activating, on a segmented phase shifter of a plurality of segmented phase shifters, one or more phase shifter segments to adjust a phase of the light in a waveguide arm of the plurality of waveguide arms, each phase shifter segment applying a respective phase adjustment to the light in the waveguide arm when activated; receiving, by a second coupler network in the GMZI, the light from the plurality of waveguide arms; combining, using the second coupler network, the light to form combined light; and outputting the combined light from one or more output ports of the GMZI,

[0133] In Example 2, the subject matter of Example 1 includes, wherein: the activating of the one or more phase shifter segments comprises applying a respective electrical stimulus to each of the one or more phase shifter segments.

[0134] In Example 3, the subject matter of Example 2 includes, wherein: the activating of the one or more phase shifter segments comprises applying to the segmented phase shifter a segment activation pattern comprising: the respective electrical stimulus applied to each of the one or more phase shifter segments; and a baseline electrical signal applied to each other phase shifter segment of the plurality of phase shifter segments.

[0135] In Example 4, the subject matter of Example 3 includes, wherein: the plurality of phase shifter segments are operable, when each phase shifter segment is activated, to collectively apply a maximum phase adjustment to the light in the waveguide arm, the maximum phase adjustment being at least 2u radians.

[0136] In Example 5, the subject matter of Example 4 includes, wherein: the plurality of phase shifter segments are operable, when each phase shifter segment is deactivated, to collectively apply zero phase adjustment to the light in the waveguide arm; and the plurality of phase shifter segments are operable to collectively apply any of a set of collective phase adjustments to the light in the waveguide arm, each collective phase adjustment corresponding to a respective segment activation pattern, the set of collective phase adjustments ranging from zero phase adjustment to the maximum phase adjustment, each phase adjustment of the set of phase adjustments being within k / 80 of each adjacent phase adjustment of the set of phase adjustments.

[0137] In Example 6, the subject matter of Examples 1-5 includes, wherein: two or more phase shifter segments of the segmented phase shifter each apply different phase adjustments from each other when activated.

[0138] In Example 7, the subject matter of Examples 3-6 includes, prior to receiving the light by the first coupler network, calibrating the segmented phase shifter by: propagating bright light through one or more light paths of the GMZI defined by the first coupler network, the waveguide arms, the second coupler network, and an output port of the one or more output ports to generate bright combined light at the output port, the one or more light paths comprising a first light path comprising the waveguide arm; detecting the bright combined light to determine an optimal phase adjustment pattern for the output port; and storing the optimal phase adjustment pattern for the output port, the optimal phase adjustment pattern being representative of an error correction phase adjustment effective to negate a respective phase error of the one or more light paths; wherein the activating of the one or more phase shifter segments comprises: retrieving the optimal phase adjustment pattern; generating the segment activation pattern based on the optimal phase adjustment pattern; and activating the one or more phase shifter segments according to the segment activation pattern to compensate for the phase error of the first light path.

[0139] In Example 8, the subject matter of Example 7 includes, wherein: the one or more light paths comprise a second light path comprising a second waveguide arm; and the method further comprises: generating a second segment activation pattern based on the optimal phase adjustment pattern; and activating zero or more phase shifter segments of a second segmented phase shifter, according to the second segment activation pattern, to adjust a phase of the light in the second waveguide arm to compensate for a phase error of the second light path.

[0140] In Example 9, the subject matter of Example 8 includes, wherein: the light is bright light.

[0141] In Example 10, the subject matter of Examples 8-9 includes, wherein: the light is a single photon.

[0142] In Example 11, the subject matter of Examples 1-10 includes, wherein: the respective phase adjustment applied by each phase shifter segment of the segmented phase shifter when activated is based on: a length of the phase shifter segment along the waveguide arm; and a voltage applied to the phase shifter segment to activate the phase shifter segment.

[0143] Example 12 is a system comprising: an integrated generalized Mach-Zehnder Interferometer (GMZI) comprising: a plurality of waveguide arms, a first coupler network configured to perform operations comprising: receiving light comprising one or more photons; and distributing the light to one or more of the plurality of waveguide arms; a second coupler network configured to perform operations comprising: receiving the light from the plurality of waveguide arms; and combining the light to form combined light; one or more output ports configured to output the combined light; and a segmented phase shifter comprising a plurality of phase shifter segments, each phase shifter segment being configured to apply a respective phase adjustment to adjust a phase of the light in a waveguide arm of the plurality of waveguide arms when activated.

[0144] In Example 13, the subject matter of Example 12 includes, wherein: each phase shifter segment is configured to receive a respective electrical stimulus to activate the phase shifter segment.

[0145] In Example 14, the subject matter of Example 13 includes, at least one controller for applying to the segmented phase shifter a segment activation pattern comprising: the respective electrical stimuli received by each of the one or more phase shifter segments, and a baseline electrical signal applied to each other phase shifter segment of the plurality of phase shifter segments.

[0146] In Example 15, the subject matter of Example 14 includes, wherein: the plurality of phase shifter segments are operable, when each phase shifter segment is activated, to collectively apply a maximum phase adjustment to the light in the waveguide arm, the maximum phase adjustment being at least 2 k radians.

[0147] In Example 16, the subject matter of Example 15 includes, wherein: the plurality of phase shifter segments are operable, when each phase shifter segment is deactivated, to collectively apply zero phase adjustment to the light in the waveguide arm; and the plurality of phase shifter segments are operable to collectively apply any of a set of collective phase adjustments to the light in the waveguide arm, each collective phase adjustment corresponding to a respective segment activation pattern, the set of collective phase adjustments ranging from zero phase adjustment to the maximum phase adjustment, each phase adjustment of the set of phase adjustments being within k / 80 of each adjacent phase adjustment of the set of phase adjustments.

[0148] In Example 17, the subject matter of Examples 12-16 includes, wherein: two or more phase shifter segments of the segmented phase shifter each apply different phase adjustments from each other when activated.

[0149] In Example 18, the subject matter of Examples 14-17 includes, a memory; wherein the at least one controller is further configured to perform operations comprising: prior to receiving the light by the first coupler network, calibrating the segmented phase shifter during a calibration stage by: propagating bright light through one or more light paths of the GMZI defined by the first coupler network, the waveguide arms, the second coupler network, and an output port of the one or more output ports to generate bright combined light at the output port, the one or more light paths comprising a first light path comprising the waveguide arm, detecting the bright combined light to determine an optimal phase adjustment pattern for the output port; and storing, in the memory, the optimal phase adjustment pattern for the output port, the optimal phase adjustment pattern being representative of an error correction phase adjustment effective to negate a respective phase error of the one or more light paths; wherein the activating of the one or more phase shifter segments comprises: retrieving, from the memory, the optimal phase adjustment pattern; generating the segment activation pattern based on the optimal phase adjustment pattern; and activating the one or more phase shifter segments according to the segment activation pattern to compensate for the phase error of the first light path.

[0150] In Example 19, the subject matter of Example 18 includes, wherein: the GMZI further comprises: a second segmented phase shifter comprising a plurality of phase shifter segments, each phase shifter segment being configured to apply a respective phase adjustment to adjust a phase of the light in a second waveguide arm of the plurality of waveguide arms when activated; and the operations performed by the at least one controller comprise: generating a second segment activation pattern based on the optimal phase adjustment pattern; and activating zero or more phase shifter segments of the second segmented phase shifter, according to the second segment activation pattern, to adjust a phase of the light in the second waveguide arm to compensate for a phase error of the second light path.

[0151] In Example 20, the subject matter of Examples 12-19 includes, wherein: the respective phase adjustment applied by each phase shifter segment of the segmented phase shifter when activated is based on: a length of the phase shifter segment along the waveguide arm; and a voltage applied to the phase shifter segment to activate the phase shifter segment.

[0152] Example 21 is a non-transitory computer readable medium comprising instructions that, when executed by at least one controller of a system, cause the system to perform the method of Example 1.

[0153] Example 22 is at least one machine-readable medium including instructions that, when executed by processing circuitry, cause the processing circuitry to perform operations to implement of any of Examples 1-21.

[0154] Example 23 is an apparatus comprising means to implement of any of Examples I--21.

[0155] Example 24 is a system to implement of any of Examples 1—21. 10156] Example 25 is a method to implement of arty of Examples 1--21.

[0157] Other technical features and example embodiments may be readily apparent to one skilled in the art from the figures, descriptions, and claims herein.

[0158] As used herein, a computer-readable storage medium refers, for example, to both machine-storage media and transmission media. Thus, the terms include both storage devices / media and carrier waves / modulated data signals. The terms “machine-readable medium,” “computer-readable medium” and “device-readable medium” mean the same thing and may be used interchangeably in this disclosure.

[0159] As used herein, a machine storage medium refers, for example, to a single or multiple storage devices and media (e.g., a centralized or distributed database, and associated caches and servers) that store executable instructions, routines and data. The term shall accordingly be taken to include, but not be limited to, solid-state memories, and optical and magnetic media, including memory internal or external to processors. Specific examples of machine-storage media, computer-storage media and devicestorage media include non-volatile memory, including by way of example semiconductor memory devices, e.g., erasable programmable read-only-memory (EPROM), electrically erasable programmable read-only memory (EEPROM), FPGA, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks The terms “machine-storage medium," "devicestorage medium," "computer-storage medium" mean the same thing and maybe used interchangeably in this disclosure. The terms "machine-storage media," "computer-storage media," and "device-storage media" specifically exclude carrier waves, modulated data signals, and other such media.

[0160] As used herein, a non-transitory computer-readable storage medium refers, for example, to a tangible medium that is capable of storing, encoding, or carrying the instructions for execution by a machine.

[0161] It will also be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first tuner could be termed a second tuner, ami, similarly, a second tuner could be termed a first tuner, without departing from the scope of the various described embodiments. The first tuner and the second tuner are both tuners, but they are not the same tuner.

[0162] The terminology used in the description of the various described embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various described embodiments and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and / or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “includes,” “including,” “comprises,” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0163] As used herein, the term “if’ is, optionally, construed to mean “when” or “upon” or “in response to determining” or “in response to detecting” or “in accordance with a determination that,” depending on the context.

[0164] The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the scope of the claims to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen in order to best explain the principles underlying the claims and their practical applications, to thereby enable others skilled in the art to best use the embodiments with various modifications as are suited to the particular uses contemplated.

Claims

I. A method for processing light in an integrated generalized Mach-Zehnder Interferometer (GMZI), the method comprising:receiving, by a first coupler network in the GMZI, light comprising one or more photons;distributing, using the first coupler network, the light to one or more of a plurality of waveguide arms in the GMZI;activating, on a segmented phase shifter of a plurality of segmented phase shifters, one or more phase shifter segments to adjust a phase of the light in a waveguide arm of the plurality of waveguide arms, each phase shifter segment applying a respective phase adjustment to the light in the waveguide arm when activated;receiving, by a second coupler network in the GMZI, the light from the plurality of waveguide arms;combining, using the second coupler network, the light to form combined light; andoutputting the combined light from one or more output ports of the GMZI.2, The method of claim 1, wherein:the activating of the one or more phase shifter segments comprises applying a respective electrical stimulus to each of the one or more phase shifter segments.

3. The method of claim 2, wherein:the activating of the one or more phase shifter segments compri ses applying to the segmented phase shifter a segment activation pattern comprising:the respective electrical stimulus applied to each of the one or more phase shifter segments; anda baseline electrical signal applied to each other phase shifter segment of the plurality of phase shifter segments.

4. The method of claim 3, wherein:the plurality of phase shifter segments are operable, when each phase shifter segment is activated, to collectively apply a maximum phase adjustment to the light in the waveguide arm, the maximum phase adjustment being at least radians.

5. The method of claim 4, wherein :the plurality of phase shifter segments are operable, when each phase shifter segment is deactivated, to collectively apply zero phase adjustment to the light in the waveguide arm; andthe plurality of phase shifter segments are operable to collectively apply any of a set of collective phase adjustments to the light in the waveguide arm, each collective phase adjustment corresponding to a respective segment activation pattern, the set of collective phase adjustments ranging from zero phase adjustment to the maximum phase adjustment, each phase adjustment of the set of phase adjustments being within ^ / 80 of each adjacent phase adjustment of the set of phase adjustments.

6. The method of claim 1, wherein:two or more phase shifter segments of the segmented phase shifter each apply different phase adjustments from each other when activated.7, The method of claim 3, further comprising:prior to receiving the light by the first coupler network, calibrating the segmented phase shifter by:propagating bright light through one or more light paths of the GMZI defined by the first coupler network, the waveguide arms, the second coupler network, and an output port of the one or more output ports to generate bright combined light at the output port, the one or more light paths comprising a first light path comprising the waveguide arm;detecting the bright combined light to determine an optimal phase adjustment pattern for the output port; andstoring the optimal phase adjustment pattern for the output port, the optimal phase adjustment pattern being representative of anerror correction phase adjustment effective to negate a respective phase error of the one or more light paths;wherein the activating of the one or more phase shifter segments comprises:retrieving the optimal phase adjustment pattern;generating the segment activation pattern based on the optimal phase adjustment pattern; andactivating the one or more phase shifter segments according to the segment activation pattern to compensate for the phase error of the first tight path.

8. The method of claim 7, wherein:the one or more light paths comprise a second tight path comprising a second waveguide arm; andthe method further comprises:generating a second segment activation pattern based on the optimal phase adjustment pattern; andactivating zero or more phase shifter segments of a second segmented phase shifter, according to the second segment activation pattern, to adjust a phase of the light in the second waveguide arm to compensate for a phase error of the second light path.

9. The method of claim 8, wherein:the light is bright light.

10. The method of claim 8, wherein:the tight is a single photon.

11. The method of claim 1, wherein:the respective phase adjustment applied by each phase shifter segment of the segmented phase shifter when activated is based on:a length of the phase shifter segment along the waveguide arm; anda voltage applied to the phase shifter segment to activate the phase shifter segment.

12. A system comprising:an integrated generalized Mach-Zehnder Interferometer (GMZI) compri sing:a plurality of waveguide arms;a first coupler network configured to perform operations comprising:receiving tight comprising one or more photons; and distributing the light to one or more of the plurality ofwaveguide arms;a second coupler network configured to perform operations comprising:receiving the light from the plurality of waveguidearms; andcombining the light to form combined light,one or more output ports configured to output the combined light; anda segmented phase shifter comprising a plurality of phase shifter segments, each phase shifter segment being configured to apply a respective phase adjustment to adjust a phase of the light in a waveguide arm of the plurality of waveguide arms when activated.

13. The system of claim 12, wherein:each phase shifter segment is configured to receive a respective electrical stimulus to activate the phase shifter segment.

14. The system of claim 13, further comprising:at least one controller for applying to the segmented phase shifter a segment activation pattern comprising:the respective electrical stimuli received by each of the one or more phase shifter segments; anda baseline electrical signal applied to each other phase shifter segment of the plurality of phase shifter segments.

15. The system of claim 14, wherein:the plurality of phase shifter segments are operable, when each phase shifter segment is activated, to collectively apply a maximum phase adjustment to the light in the waveguide arm, the maximum phase adjustment being at least radians.

16. The system of claim 15, wherein:the plurality of phase shifter segments are operable, when each phase shifter segment is deactivated, to collectively apply zero phase adjustment to the light in the waveguide arm; andthe plurality of phase shifter segments are operable to collectively apply any of a set of collective phase adjustments to the light in the waveguide arm, each collective phase adjustment corresponding to a respective segment activation pattern, the set of collective phase adjustments ranging from zero phase adjustment to the maximum phase adjustment, each phase adjustment of the set of phase adjustments being within ^ / 80 of each adjacent phase adjustment of the set of phase adjustments.

17. The sy stem of claim 12, wherein:two or more phase shifter segments of the segmented phase shifter each apply different phase adjustments from each other when activated.

18. The system of claim 14,further comprising a memory;wherein the at least one controller is further configured to perform operations comprising:prior to receiving the light by the first coupler network, calibrating the segmented phase shifter during a calibration stage by:propagating bright light through one or more lightpaths of the GMZI defined by the first coupler network, the waveguide arms, the second coupler network, and an output port of the one or more output ports to generate bright combined light at the output port, the one or more light paths comprising a first light path comprising the waveguide arm,detecting the bright combined light to determine an optimal phase adjustment pattern for the output port; andstoring, in the memory, the optimal phase adjustment pattern for the output port, the optimal phase adjustment pattern being representative of an error correction phase adjustment effective to negate a respective phase error of the one or more light paths;wherein the activating of the one or more phase shifter segments comprises:retrieving, from the memory, the optimal phase adjustment pattern;generating the segment activation pattern based on the optimal phase adjustment pattern; andactivating the one or more phase shifter segments according to the segment activation pattern to compensate for the phase error of the first light path.

19. The system of claim 18, wherein:the GMZI further comprises:a second segmented phase shifter comprising a plurality of phase shifter segments, each phase shifter segment being configured to apply a respective phase adjustment to adjust a phase of the light in a second waveguide arm of the plurality of waveguide arms when activated; andthe operations performed by the at least one controller comprise:generating a second segment activation pattern based on the optimal phase adjustment pattern, andactivating zero or more phase shifter segments of the second segmented phase shifter, according to the second segment activation pattern, to adjust a phase of the light in the second waveguide arm to compensate for a phase error of the second light path.

20. The system of claim 12, wherein:the respective phase adjustment applied by each phase shifter segment of the segmented phase shifter when activated is based on:a length of the phase shifter segment along the waveguide arm; anda voltage applied to the phase shifter segment to activate the phase shifter segment.

21. A non-transitory computer readable medium comprising instructions that, when executed by at least one controller of a system, cause the system to perform the method of claim 1.

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