Demultiplexer and method of use thereof

Abstract

We generally describe an optical demultiplexer, comprising: an electro-optic modulator for changing the polarization of an optical pulse having a first polarization and passing through the electro-optic modulator from the first polarization to a second polarization when the electro-optic modulator is in a first state; a first mirror and a second mirror, wherein the electro-optic modulator is located in an optical track between the first mirror and the second mirror, such that an optical pulse traveling in the optical track between the first mirror and the second mirror passes through the electro-optic modulator, wherein the first mirror and the second mirror are located in the optical demultiplexer, such that an optical pulse traveling in the optical track between the first mirror and the second mirror passes through the electro-optic modulator. The pulse, during each round of travel between the first and second mirrors, is shifted perpendicular to the propagation direction of the light pulse between the first and second mirrors; and a first polarization beamsplitter is located in the optical track between the first mirror and the electro-optic modulator, wherein the first polarization beamsplitter is configured to: transmit a light pulse having a first polarization and reflect a light pulse having a second polarization to remove a light pulse having a second polarization from the optical track between the first and second mirrors, wherein the first polarization beamsplitter is configured to reflect light pulses that are shifted perpendicular to each other's propagation direction onto different, respective output tracks.

Description

Technical Field

[0001] The present invention generally relates to a demultiplexer, specifically, the demultiplexer uses a single active element to send any number of time patterns under the same spatial mode toward different synchronization spatial modes. Background Technology

[0002] In photonics, typically involving both classical and quantum states, various properties of light are manipulated, such as, but not limited to, polarization and temporal and spatial information. Given the increasing complexity of photonic platforms, it may be necessary to increase the number of modes that can be manipulated simultaneously. In some methods according to existing techniques, when aiming to generate multiple simultaneous modes, one can start with a single spatial mode containing a stream of optical pulses, and then demultiplex that stream of pulses in time to space. This results in (non-simultaneous) pulses being routed to different, synchronous (simultaneous) spatial modes.

[0003] Demultiplexing protocols can be used in photonic (optical) quantum computing, in which demultiplexed signals are generated from multi-photon sources and can be used to process quantum information, thereby enabling quantum computing.

[0004] Figure 1 illustrates a demultiplexer method according to the prior art. In this example, in demultiplexer 100, light from a single-photon source (i.e., a stream of independent particles of light traveling in the same spatial mode (e.g., optical fiber)) first passes through an active element, causing the photon polarization to alternate between two orthogonal polarization states. In this example, the active element is a Pockels cell 102. Subsequently, the photon passes through a polarization beamsplitter 104, which classifies the photon according to its polarization. This results in two spatial modes for the single photon. This process can be repeated in a network of Pockels cells (e.g., Pockels cells 106, 110) and polarization beamsplitters (e.g., polarization beamsplitters 108, 112), whereby different photons with different polarizations can be reflected by mirrors (e.g., mirror 114) toward different output paths.

[0005] In this example, for instance, laser pulses occurring every 12.5 ns pass through a series of electro-optic modulators (in this example, Pockels units) and polarization beamsplitters to actively route to different spatial outputs.

[0006] Optical delay is applied to one or more outputs to correct for time mismatches between these outputs. For example, time delay can be achieved by applying optical fibers at the outputs to correct and match the arrival times of different photons.

[0007] Using the method shown in Figure 1, a single-photon source is demultiplexed into a synchronous two-photon source in the first stage of the Pockels unit 102 and the polarization beam splitter 104. As in the example of Figure 1, the above process can be repeated for each newly created spatial mode so that an active element is added each time to create a multi-output spatial mode, thereby producing a demultiplexed multiphoton source.

[0008] In this example, the number of active components required is equal to the number of target output modes minus 1.

[0009] Based on sources with up to, for example, 10 to 20 photon modes, demultiplexed photon modes can be used in photonic quantum computing experiments. The generation of these photon modes can be experimentally challenging because it requires many active components that can occupy a considerable amount of space in a laboratory, and each active component typically requires expensive high-voltage pulses, the synchronization of which is challenging.

[0010] Therefore, an improved demultiplexer is needed. Summary of the Invention

[0011] According to this disclosure, an optical demultiplexer is provided. The optical demultiplexer includes an electro-optic modulator, which, when in a first state, changes the polarization of an optical pulse having a first polarization and passing through the electro-optic modulator from the first polarization to a second polarization. Here, the polarization of the optical pulse may refer to the polarization state of the optical pulse, and when the polarization state of the optical pulse is related to an optical pulse having a first polarization, the electro-optic modulator is used to change the polarization state of the optical pulse so that the optical pulse has a second polarization when leaving the electro-optic modulator. The optical demultiplexer further includes a first mirror and a second mirror, wherein an electro-optic modulator is located in an optical track between the first and second mirrors such that an optical pulse traveling in the optical track between the first and second mirrors passes through the electro-optic modulator. The first and second mirrors are located in the optical demultiplexer such that the optical pulse traveling in the optical track between the first and second mirrors is shifted between the first and second mirrors perpendicular to the propagation direction of the optical pulse during each round of travel between the first and second mirrors. The optical demultiplexer further includes a first polarization beamsplitter located in the optical track between the first mirror and the electro-optic modulator. The first polarization beamsplitter is used to: transmit an optical pulse with a first polarization and reflect an optical pulse with a second polarization to remove an optical pulse with a second polarization from the optical track between the first and second mirrors. The first polarization beamsplitter is used to reflect optical pulses shifted relative to each other perpendicular to their propagation directions onto different corresponding output tracks. The state of the electro-optic modulator can be controlled to determine whether the optical pulse has a first polarization so that a first polarization beamsplitter transmits the optical pulse, or whether the optical pulse has a second polarization so that the first polarization beamsplitter reflects the optical pulse. In some examples, when the electro-optic modulator is in the first state, the electro-optic modulator is turned on, such that when the optical pulse travels through the electro-optic modulator, the polarization state of the optical pulse with the first polarization changes to the second polarization.

[0012] The optical demultiplexer described in this paper reduces the technical burden required to generate operational demultiplexed multiphoton sources. Multiple high-voltage pulse generators are no longer needed, thus reducing the cost and space required to fabricate multiphoton sources.

[0013] An electro-optic modulator can switch the polarization of an optical pulse. Once switched, a beam splitter can reflect the optical pulse to remove it from the optical track between the first and second mirrors.

[0014] Once the light pulse is shifted between the mirrors relative to each other in a direction perpendicular to the propagation direction, the light pulse can be reflected by the beam splitter onto different corresponding output trajectories.

[0015] It should be noted that, given that light pulses are generated with time intervals between them and are therefore “displaced” relative to each other, light pulses can be displaced relative to each other. If such light pulses were not displaced relative to each other perpendicular to the direction of propagation between the mirrors, such light pulses could end up on the same output trajectory (possibly at different times).

[0016] In some examples, the electro-optic module can be a modulator utilizing the electro-optic effect of certain electro-optic crystals, such as, but not limited to, lithium niobate (LiNbO3), gallium arsenide (GaAs), and lithium tantalate (LiTaO3). The electro-optic effect occurs when a voltage is applied to the electro-optic crystal, causing a change in the crystal's refractive index, which in turn alters the crystal's photoportability, enabling modulation of the phase, amplitude, intensity, and polarization state of the optical signal.

[0017] In some examples, polarization beam splitters, such as, but not limited to, Wollaston prisms, can use birefringent materials to split light into two beams with orthogonal polarization states. Birefringent materials can be a relatively simple and inexpensive way to split light into a reflected beam (e.g., S-polarized) and a transmitted beam (e.g., P-polarized).

[0018] In some preferred implementations, the demultiplexer further includes a second polarization beamsplitter located in an optical track between the second mirror and the electro-optic modulator. The second polarization beamsplitter is used to: transmit light pulses with a first polarization and reflect light pulses with a second polarization to remove light pulses with a second polarization from the optical track between the first and second mirrors (based on the electro-optic modulator having switched the polarization of the light pulses from the first to the second polarization). The second polarization beamsplitter is used to reflect light pulses that are shifted relative to each other perpendicular to their propagation directions onto different corresponding output tracks. Providing a second polarization beamsplitter as described above may be particularly advantageous because it can increase (in some examples, double) the number of output beams.

[0019] In some preferred implementations, the demultiplexer further includes a first converging lens located in an optical track between the electro-optic modulator and the first polarizing beamsplitter. The first converging lens is used to converge optical pulses traveling in the optical track from the electro-optic modulator to the first converging lens, such that optical pulses displaced relative to each other perpendicular to their propagation directions travel parallel to each other between the first converging lens and the first polarizing beamsplitter. This allows optical pulses removed from the optical track between the first and second mirrors to travel parallel once reflected onto different corresponding output tracks, which simplifies further use of the optical pulses (e.g., if precise timing of when a corresponding optical pulse is reflected onto its corresponding output track is required).

[0020] In some preferred implementations, the demultiplexer further includes a second converging lens located in an optical track between the electro-optic modulator and the second mirror. The second converging lens is used to converge optical pulses traveling in the optical track from the electro-optic modulator to the second converging lens, such that optical pulses displaced relative to each other perpendicular to their propagation directions travel parallel to each other between the second converging lens and the second mirror. This allows optical pulses removed from the optical track between the first and second mirrors to travel parallel once reflected onto different corresponding output tracks, which simplifies further use of the optical pulses (e.g., if precise timing of when a corresponding optical pulse is reflected onto its corresponding output track is required).

[0021] In some preferred implementations, a second converging lens is located in an optical track between the electro-optic modulator and the second polarizing beamsplitter. The second converging lens is used to converge light pulses traveling in the optical track from the electro-optic modulator to the second converging lens, such that light pulses displaced relative to each other perpendicular to their propagation directions travel parallel to each other between the second converging lens and the second polarizing beamsplitter. This allows light pulses removed from the optical track between the first and second mirrors to travel parallel once reflected onto different corresponding output tracks, which simplifies further use of the light pulses (e.g., if precise timing of when a corresponding light pulse is reflected onto its corresponding output track is required).

[0022] In some preferred implementations, the first and second converging lenses are located in the optical demultiplexer in a telescope configuration with unity magnification. This allows for a more constrained optical demultiplexer, thereby further reducing the space required to fabricate multiphoton sources.

[0023] In some preferred implementations, a light pulse traveling in an optical path between the first and second mirrors enters the input path of the optical demultiplexer, is aligned parallel to and displaced from the central axis of the telescope configuration. This is a simple way to supply a light beam to the optical demultiplexer, wherein the beam is displaced perpendicular to its propagation direction as it travels back and forth between the two mirrors.

[0024] In some preferred implementations, the electro-optic modulator is located at the center or central region of the telescope structure. This allows for switching beam polarization for all beams traveling back and forth between the two mirrors, while the electro-optic modulator can be confined to a (small) space located at the center or central region of the telescope structure.

[0025] In some preferred implementations, the first reflector includes a first reflector assembly and a second reflector assembly for reflecting light pulses traveling in an optical path from the first converging lens to the first reflector. The first and second reflector assemblies are aligned perpendicularly or substantially perpendicularly to each other, and are aligned at an angle of 45 degrees or approximately 45 degrees relative to an optical path along which the light pulses travel parallel to each other between the first converging lens and the first reflector. This allows for a simple and cost-effective way to ensure that the light beam is shifted between the two reflectors in a direction perpendicular to the propagation direction, ultimately reflecting the beam onto different corresponding output paths via a beam splitter.

[0026] In some preferred implementations, the second reflector includes a third and a fourth reflector assembly for reflecting light pulses traveling in an optical path from the second converging lens to the second reflector. The third and fourth reflector assemblies are aligned perpendicularly or substantially perpendicularly to each other, and are aligned at an angle of 45 degrees or approximately 45 degrees relative to an optical path along which the light pulses travel parallel to each other between the second converging lens and the second reflector. This further allows for a simple and cost-effective method to ensure that the light beam is shifted between the two reflectors in a direction perpendicular to the propagation direction, ultimately reflecting the beam onto different, respective output paths via a beam splitter.

[0027] In some preferred implementations, one or both of the first and second mirrors include an opening that allows light pulses to be provided into an optical track between the first and second mirrors. This can be provided in any one or more exemplary implementations outlined throughout this disclosure and allows for a simple and cost-effective way to provide a light beam to the optical demultiplexer in a desired manner.

[0028] In some preferred implementations, the demultiplexer further includes a third mirror positioned at the end of the optical track with normal incidence relative to the end of the optical track, such that the reflected light pulses travel in opposite directions between the first and second mirrors. This can be particularly advantageous because the number of light pulses output to different, respective output tracks can be doubled.

[0029] In some preferred implementations, an optical demultiplexer is used to remove optical pulses with different temporal modes and the same spatial mode from the optical trajectory to different spatial modes via a first polarization beamsplitter when the electro-optic modulator is switched from a second state to a first state. In the second state, the polarization of the optical pulse with the first polarization does not change as the optical pulse passes through the electro-optic modulator, thereby allowing the optical pulses, which originally had different temporal modes and the same spatial mode, to be used independently of each other. This can be provided in any one or more exemplary implementations outlined throughout this disclosure.

[0030] In some preferred implementations, based on the fact that all optical pulses traveling on the optical track between the first and second mirrors have a first polarization, and based on the fact that the electro-optic modulator switches from a second state to a first state such that when all optical pulses travel past the electro-optic modulator in the first state, the polarization of all optical pulses changes from the first polarization to the second polarization, a first polarization beamsplitter is used to remove all optical pulses from the optical track between the first and second mirrors simultaneously or within less than 10 nanoseconds. This ensures that in an 80 MHz repetition rate system, the modulation switching time is less than the standard 12.5 ns. This can be provided in any one or more exemplary implementations outlined throughout this disclosure.

[0031] In some preferred implementations, when the electro-optic modulator switches from a second state to a first state, a first polarization beamsplitter removes all optical pulses from the optical track between the first and second mirrors simultaneously or within less than 10 nanoseconds and reflects all optical pulses onto different corresponding output tracks, each of which contains a single optical pulse from the optical pulses. This ensures that, in an 80 MHz repetition rate system, the modulation switching time is less than the standard 12.5 ns. This can be provided in any one or more exemplary implementations outlined throughout this disclosure.

[0032] In some preferred implementations, the electro-optic modulator includes a Pockels cell, wherein a first state is associated with the Pockels cell being turned on. Pockels cells can be particularly advantageous because they allow for ultrafast and precise optical modulation. A Pockels cell can be defined as an electro-optic modulation device utilizing the Pockels effect. The Pockels effect refers to a photoelectric phenomenon in which the refractive index of a particular crystal is proportional to the electric field strength. By controlling an external electric field, the refractive index in a certain direction can be changed, allowing the Pockels cell to operate as a variable half-wave chip, thereby achieving a change in polarization state.

[0033] In some preferred implementations, the electro-optic modulator is capable of switching between a first state and a second state in less than 10 nanoseconds, wherein in the first state, the polarization of a light pulse with a first polarization changes as the light pulse passes through the electro-optic modulator, and in the second state, the polarization of a light pulse with the first polarization does not change as the light pulse passes through the electro-optic modulator. This ensures that, in an 80 MHz repetition rate system, the modulation switching time is less than the standard 12.5 ns. This can be provided in any one or more exemplary implementations outlined throughout this disclosure.

[0034] In some preferred implementations, the demultiplexer further includes a set of additional mirrors located within the optical track to confine the optical track to an area of ​​1.5 meters (or less) by 0.5 meters (or less) for a track length of at least 6 meters. This further reduces the space required for the optical demultiplexer, particularly achieving cost savings.

[0035] Furthermore, a quantum computing system is provided, which includes an optical demultiplexer as described herein, and in particular any of the implementations described above.

[0036] Furthermore, a system, particularly a quantum computing system, is provided, comprising: an optical demultiplexer as described herein, particularly any of the implementations described above; a single-photon source for generating a single-photon stream, wherein the single-photon source is coupled to the optical demultiplexer to provide the single-photon stream to the optical demultiplexer, and wherein the optical demultiplexer is used to output multiple indistinguishable single photons correspondingly to corresponding output trajectories in different output trajectories. Here, indistinguishable single photons can be generated without using multiple high-voltage pulse generators, thereby reducing the cost and space required to fabricate multiphoton sources.

[0037] A further method is provided for correspondingly outputting multiple single photons onto corresponding output trajectories in different output trajectories. This method includes: providing a system as described herein, particularly any of the implementations described above; providing multiple light pulses with a first polarization into the optical trajectory between the first and second mirrors via a single photon source, aligned parallel to and shifted from the central axis of the optical trajectory between the first and second mirrors; switching an electro-optic modulator from a second state to a first state, wherein in the second state, the polarization of the light pulses with the first polarization does not change as the light pulses pass through the electro-optic modulator, and the first state causes the polarization of the light pulses to change from the first polarization to the second polarization; and reflecting the light pulses with the second polarization based on a first polarization beamsplitter to remove the light pulses from the optical trajectory between the first and second mirrors, thereby correspondingly outputting multiple single photons onto corresponding output trajectories in different output trajectories. As described above, the light pulses can be generated without using multiple high-voltage pulse generators, thereby reducing the cost and space required to fabricate a multiphoton source.

[0038] In some preferred implementations, one or more optical pulses travel back and forth multiple times between the first and second reflectors, wherein the electro-optic modulator switches from a second state to a first state while one of the optical pulses travels its final round of back and forth travel between the first and second reflectors. This allows a predetermined number of optical pulses to be output onto different corresponding output trajectories. Additionally or alternatively, the beam lateral spatial width of the optical pulses provided by a single photon source is 2 mm or approximately 2 mm (related to 1 / e intensity), which allows maintaining a Rayleigh range of several meters (this may be important in some examples, as the typical interval between optical pulses in a fixed time frame is approximately 12.5 ns, i.e., approximately 4 m).

[0039] A further method is provided for performing quantum computing based on (i) optical pulses or (ii) multiple single photons, wherein the optical pulses are reflected / output to different output trajectories using an optical demultiplexer or quantum computing system as described herein, particularly any of the exemplary implementations described above, and the multiple single photons are correspondingly output to corresponding output trajectories in the different output trajectories using a system as described herein, particularly any of the exemplary implementations described above.

[0040] A further provision provides a computer program product including a program code portion, which, when executed on one or more computing devices, performs the methods described above. In some preferred examples, the computer program product is stored on a computer-readable recording medium.

[0041] Based on the exemplary implementation described herein, the scalability problem in time-space demultiplexers is addressed. Quasi-regressive geometry can be used to path the input single-photon source, enabling the input source to be demultiplexed into any number of output modes using only a single active element. The resulting demultiplexed modes are synchronized through construction, eliminating the need for further optical delays.

[0042] Throughout this disclosure, an active (optical) element can refer to an electronic component that alters the motion properties (e.g., polarization, amplitude, etc.) of photons using electrical energy. In some examples, an active element is, for instance, an electro-optic modulator, such as an electro-optic modulated Pockels unit.

[0043] Using the exemplary implementation described herein reduces the technical burden required to generate a functional demultiplexed multiphoton source. It overcomes the challenging manipulation of many high-voltage pulse generators. Therefore, the implementation described herein allows for reduced costs while minimizing the volume and space required in the laboratory. Attached Figure Description

[0044] These and other aspects of the invention will now be further described by way of example only, with reference to the accompanying drawings, wherein like reference numerals refer to like parts, in which:

[0045] Figure 1 shows a schematic diagram of a demultiplexer according to the prior art;

[0046] Figures 2a to 2d A schematic diagram of a demultiplexer according to some exemplary implementations of this disclosure is shown. Figure 2e It shows Figure 2d Spatial output distribution of the multiplexer mode;

[0047] Figure 3 A schematic diagram of a demultiplexer according to some exemplary implementations of this disclosure is shown;

[0048] Figure 4 A schematic block diagram of a system according to some exemplary implementations of this disclosure is shown;

[0049] Figure 5 Flowcharts of methods according to some exemplary implementations of this disclosure are shown; and

[0050] Figure 6 A flowchart of a method according to some exemplary implementations of this disclosure is shown. Detailed Implementation

[0051] This disclosure generally relates to a resource-efficient active time-space demultiplexer.

[0052] A demultiplexer module is proposed. Depending on the implementation, this module requires only a single active element to route any number of time patterns within the same spatial mode to different synchronous spatial modes. A stream of optical pulses traveling in the same spatial trajectory can be converted into multiple trajectories, each containing a single pulse simultaneously.

[0053] According to some exemplary implementations of this disclosure, demultiplexers are typically constructed using three main optical elements: one or more polarization beam splitters (PBS), a highly reflective mirror, and an ultrafast electro-optic modulator (e.g., a Pockels unit) with a switching rate, for example, greater than 10 MHz.

[0054] When using a demultiplexer according to an exemplary implementation as described herein, the demultiplexer can operate in both a "loading" phase and a "releasing" phase. In the "loading" phase, as long as the electro-optic modulator remains in its off state, the demultiplexer module is used for the input path of the photon source to traverse a gradually increasing quasi-regressive geometry. In the "releasing" phase, the electro-optic modulator is switched to its on state, which causes a polarization reversal of all optical pulses traveling through the electro-optic modulator, thereby allowing each pulse to simultaneously present a different output trajectory.

[0055] In some exemplary implementations of the time-space demultiplexer according to this disclosure, the number of active elements required to demultiplex N pulses has been reduced from N (as in existing alternatives) to only one active element, which is generally independent of N. Here, N may represent the number of pulses to be multiplexed, and according to some exemplary implementations of this disclosure, the number of pulses to be multiplexed may depend solely on the size of the optics used. As a result, in the exemplary implementations according to this disclosure, the number of typically relatively expensive high-voltage amplifiers is reduced, potentially requiring the use of fewer birefringent crystals, and complex electronics for multi-pulse synchronization can be avoided.

[0056] Figures 2a to 2d A schematic diagram of a demultiplexer 200 according to some exemplary implementations of this disclosure is shown.

[0057] In this example, if it is possible Figure 2a As seen in the image, the demultiplexer 200 typically includes an electro-optic modulator (EOM) 202, a first mirror 204, and a second mirror 206. In this example, the first mirror 204 includes a first mirror assembly 204a and a second mirror assembly 204b. Furthermore, in this example, the second mirror 206 includes a third mirror assembly 206a and a fourth mirror assembly 206b.

[0058] To ultimately couple light out of the optical track 208 between the first mirror 204 and the second mirror 206, a first polarizing beam splitter 210 and a second polarizing beam splitter 212 are provided. However, as will be understood, a single polarizing beam splitter may be sufficient to couple light out of the optical track 208 between the first mirror 204 and the second mirror 206.

[0059] In this example, the first converging lens 214 is located in the optical track between the electro-optic modulator 202 and the first polling beam splitter 210, and the second converging lens 216 is located in the optical track between the electro-optic modulator 202 and the second polarization beam splitter 212.

[0060] In this example, the input path 218 of the demultiplexer 200, through which the light source (photons, denoted using the Dirac notation |h>) enters, is aligned parallel-displacedly with the central axis of the telescope configuration formed by the first converging lens 214 and the second converging lens 216, which in this example are identical lenses, and where the telescope configuration exhibits unity magnification. This slightly parallel-displaced alignment of the input path 218 with respect to the central axis of the unity-magnification telescope configuration causes the displacement to be mirrored in the opposite direction at the telescope's output. This produces a quasi-regressive geometry for the input beam trajectory.

[0061] In this example, the center (or central region) of the telescope contains an active electro-optic modulator 202 (in some examples, a Pockels unit), and the telescope itself is placed within polarization beams 210 and 212.

[0062] In this example, the reflector 220 is located at the end of the optical path so that all beams return in the direction of backward travel, thereby doubling the number of output modes, as will be described further below.

[0063] According to such Figure 2a In the arrangement shown, in the first step of the demultiplexer method according to this disclosure, in some examples, for example, a horizontally polarized light pulse can pass through a polarization beam splitter 212, a telescope made of two converging lenses 214 and 216, and an electro-optic modulator 202.

[0064] like Figure 2b As shown, mirrors 204 and 206 and their respective components are used to align the beam trajectory so that after passing through the polarizing beam splitter, converging lens, and electro-optic modulator, the light returns to the setup with a parallel-shifted trajectory, but now travels in the opposite direction, provided the electro-optic modulator remains off. Figure 2b(Paths 2, 4, 6, and 8 are shown). This process itself continues to repeat multiple times, while the electro-optic modulator remains off as long as the effective aperture of the optical element allows. Therefore, the optical trajectory continues to be constructed with a quasi-regressive geometry, and in this example, the light polarization remains horizontal.

[0065] If already Figure 2a As shown in the illustration, reflector 220 is positioned at the end of the optical trajectory with normal incidence in this example, such that all beams return again in the direction of backward travel. Therefore, for the same effective aperture size, the number of output modes is doubled (16 modes in this example), as can be seen in... Figure 2c What I saw in the video.

[0066] Figures 2a to 2c The process shown completes the "loading" phase of the optical pulse to be demultiplexed according to some protocols of this disclosure.

[0067] During the "release" phase of the protocol, the electro-optic modulator 202 is activated, causing the polarization of the optical pulse to rotate, in this example, to its perpendicular direction. Therefore, in this example, polarization beam splitters 210 and 212 reflect the optical pulse, releasing it from its original optical trajectory, thus completing the demultiplexing protocol (see [link to protocol]). Figure 2d All initial time delays between input optical pulses are erased by the geometry itself, ensuring that all optical pulses remain synchronized. Therefore, the optical pulses are released onto different (synchronized) output tracks, generating demultiplexed signals.

[0068] If the input light consists of a single-photon stream, a demultiplexer allows the fabrication of multiple indistinguishable single-photon sources. For example, in protocols for photonic quantum computing, multiple indistinguishable single-photon sources are prepared to be inserted into a multimode interferometer and interfered with within it. Therefore, a key application of demultiplexers is the construction of multiphoton sources for optical quantum information processing; however, as those skilled in the art will understand, other applications are possible.

[0069] The technical parameters that need to be considered in demultiplexing are optical loss, passive and active polarization contrast, beam trajectory space width, effective aperture, and rise time of electro-optic modulator (Poukes unit).

[0070] In some examples of demultiplexers, the mirrors exhibit reflectivity greater than 99.99% (i.e., a loss of less than 0.01% per element). Additionally or alternatively, polarization beamsplitters exhibit a loss of less than 1% per element. Additionally or alternatively, converging lenses have a loss of less than 1% per element. Additionally or alternatively, electro-optic modulators have a loss of less than 1% per element.

[0071] In some examples, the polarization contrast (the ratio between the transmission (reflection) of s-polarized light and the transmission (reflection) of p-polarized light in the polarization beamsplitter is greater than 1000:1 for both the transmission and reflection ports. Furthermore, in some examples, the electro-optic modulator can achieve an active polarization contrast greater than 100:1.

[0072] In some examples, the transverse width of the beam can be varied, and in some examples, it can be chosen to be approximately 2 mm in diameter (related to 1 / e intensity), thus maintaining a Rayleigh range of several meters. This may be important because the typical interval between light pulses in a fixed time frame is approximately 12.5 ns, i.e., approximately 4 m. Here, the Rayleigh range can refer to the distance from the waist of the beam along the beam path to a cross-section twice its area, where the radius of the cross-section is approximately 1.414 times the radius of the waist. √ 2).

[0073] In some examples, the mirror has a size of 1 inch or approximately 1 inch, and / or the polarizing beam splitter has a size of 1 inch or approximately 1 inch. In some examples, the two converging lenses have a focal length of 300 mm and an aperture size of 2 inches. In examples where an increased effective aperture is required, for example, several polarizing beam splitters may be stacked adjacent to each other to achieve a larger effective aperture.

[0074] In some examples, the electro-optic modulator (e.g., a Pockels unit) can switch from an off state to an on state (and / or from an on state to an off state) in less than 10 ns. This ensures that the modulation switching time is less than the standard 12.5 ns in an 80 MHz repetition rate system. In some examples, the drive switching voltage along the Pockels unit is approximately 1 kV.

[0075] To test the conceptual geometry of the demultiplexer, such as Figure 2d As shown, a smaller version of the demultiplexer is constructed using only standard 1-inch optical components, resulting in 16 output spatial modes. All 16 output spatial modes are similar to the input modes, as can be seen in... Figure 2e As seen in the image, this ensures that all 16 outputs can be collected with high fiber coupling efficiency (i.e., allowing high collection efficiency in single-mode fiber).

[0076] Among the parameters mentioned above, the rise time of the active element directly affects the system size. This is because the traveling optical pulse must switch its polarization within the last round trip of its trajectory, meaning that the (time-equivalent) space of each round trip should be smaller than the interval between pulses. Existing commercially available Pockels units can switch optical polarization with a switching time of approximately 10 ns. Therefore, standard laser / optical systems with a repetition rate of 80 MHz (12.5 ns pulse interval) can be used.

[0077] However, as will be understood, for a light pulse, a time of 12.5 ns is equivalent to 3.75 m of free space, thus in Figure 2d The alignment results in an implementation approximately 8m long. To avoid this, additional reflectors 320a to 320h can be implemented, such as... Figure 3 As shown in the demultiplexer 300, these additional mirrors do not change the conceptual operation of the demultiplexer, but help to reduce the footprint. In some examples, the demultiplexer has a size of approximately 1.5m by 0.5m; in this example, it is for a 12-output demultiplexer.

[0078] Figure 4 A schematic block diagram of a system 400 according to some exemplary implementations of this disclosure is shown.

[0079] In this example, demultiplexers 200 and 300 are included in system 400 (which may be a quantum computing system) together with a single-photon source 402 for generating a single-photon stream. The single-photon source 402 is coupled to the optical demultiplexers 200 and 300 to provide a single-photon stream to the optical demultiplexers 200 and 300. In system 400, the demultiplexers 200 and 300 are used to output multiple indistinguishable single photons correspondingly to different output trajectories.

[0080] Figure 5 A flowchart of a method 500 according to some exemplary implementations of this disclosure is shown.

[0081] Method 500 includes, at step 502, providing a system, particularly a quantum computing system, comprising an optical demultiplexer and a single-photon source, the optical demultiplexer comprising: an electro-optic modulator for changing the polarization of an optical pulse having a first polarization and passing through the electro-optic modulator from the first polarization to a second polarization when the electro-optic modulator is in a first state; a first mirror and a second mirror, wherein the electro-optic modulator is located in an optical track between the first mirror and the second mirror such that an optical pulse traveling in the optical track between the first mirror and the second mirror passes through the electro-optic modulator, wherein the first mirror and the second mirror are located in the optical demultiplexer such that an optical pulse traveling in the optical track between the first mirror and the second mirror is shifted during each round of travel between the first mirror and the second mirror; and a first polarization beam splitter. The device, located in an optical track between a first reflector and an electro-optic modulator, wherein the first polarization beamsplitter is used to: transmit light pulses with a first polarization and reflect light pulses with a second polarization, to separate light pulses with a second polarization from the optical track between the first and second reflectors based on the electro-optic modulator having switched the polarization of the light pulses from the first polarization to the second polarization, wherein the first polarization beamsplitter is used to separate light pulses that are displaced relative to each other from the optical track between the first and second reflectors to different output tracks; and a single-photon source for generating a single-photon stream, wherein the single-photon source is coupled to an optical demultiplexer to provide a single-photon stream to the optical demultiplexer, and wherein the optical demultiplexer is used to output multiple indistinguishable single photons correspondingly to corresponding output tracks in different output tracks.

[0082] At step 504, method 500 includes: providing a plurality of light pulses having a first polarization into the optical track between the first and second mirrors via a single photon source, in a manner aligned parallel to and displaced from the central axis of the optical track between the first and second mirrors.

[0083] At step 506, method 500 includes: switching the electro-optic modulator from a second state to a first state, wherein in the second state, the polarization of a light pulse having a first polarization does not change as the light pulse passes through the electro-optic modulator, and in the first state, the polarization of the light pulse changes from the first polarization to the second polarization.

[0084] At step 508, method 500 includes: reflecting a light pulse with a second polarization based on a first polarizing beamsplitter, and correspondingly outputting multiple single photons onto corresponding output trajectories in different output trajectories to remove the light pulse from the optical trajectory between the first and second mirrors. The light pulse can be correspondingly output onto the corresponding output trajectory.

[0085] In some examples, the transverse spatial width of the light pulses provided by a single photon source can be 2 millimeters or approximately 2 millimeters.

[0086] Figure 6 A flowchart of a method 600 according to some exemplary implementations of this disclosure is shown.

[0087] At step 602, a demultiplexer or system according to any of the exemplary implementations described herein is provided. At step 604, a quantum computing operation is performed based on (i) optical pulses output to different output trajectories using an optical demultiplexer according to any of the exemplary implementations described herein, or (ii) multiple single photons correspondingly output to corresponding output trajectories in different output trajectories using a system according to any of the exemplary implementations described herein.

[0088] The module for time-space demultiplexing according to this disclosure uses a single active element to route any number of time modes within the same spatial mode to different synchronous output spatial modes. The stream of all optical pulses passing through the demultiplexer in the same spatial mode is converted into multiple output tracks, each with one such pulse simultaneously.

[0089] In some examples, the demultiplexer comprises three types of optical elements: one or more polarization beamsplitters for spatially classifying orthogonal polarizations; highly reflective mirrors (with reflectivity, for example, greater than 99.99%); and a (ultrafast) electro-optic modulator, particularly in the form of a Pockels cell, operating at speeds greater than 10 MHz. Conceptually, as described above, the protocol is divided into a "loading" phase and a "releasing" phase. In the former phase, the input (laser) pulse travels through a gradually increasing and quasi-regressing geometry while the electro-optic modulator (Pockels cell) remains off. In the latter phase, the electro-optic modulator (Pockels cell) is turned on, which flips the polarization of each pulse to an orthogonal state, now allowing the pulses to be released from the regression geometry, each pulse leaving the device with its own distinct synchronous trajectory.

[0090] In the device according to this disclosure, the number of active elements required to demultiplex N pulses is reduced to a single active element (as is typically N-1 active elements in existing alternatives). The number of demultiplexable modes is conceptually arbitrary, and in practice limited only by the finite aperture of the optical elements used. Using the method proposed herein, typically expensive high-voltage amplifiers and drivers, birefringent crystals, and complex multipulse electronics are reduced to only one in each case, resulting in lower cost, smaller footprint, and ease of implementation. With appropriate effective aperture, a demultiplexer according to the exemplary implementation described herein can be used to demultiplex dozens of outputs while always occupying the same footprint.

[0091] As mentioned above, a key application of demultiplexers is therefore the construction of multiphoton sources for optical quantum information processing; however, as those skilled in the art will understand, other applications are possible. In this regard, quantum computing can be achieved by encoding the computational process into specific, complex entangled states through the manipulation and measurement of entangled states (including quantum state tuning) in a specific order. Measurement-based quantum computing is a resource state based on highly entangled cluster states. The computation itself can be achieved by continuously measuring neighboring qubits from the cluster state. By efficiently implementing arbitrary single-qubit and two-qubit (or multi-qubit) operations, the measurement sequence, along with the measurement device, can define a computer system for general-purpose quantum computing.

[0092] Undoubtedly, those skilled in the art will conceive of many other effective alternatives. It should be understood that the invention is not limited to the described embodiments, but includes modifications that are obvious to those skilled in the art and fall within the scope of the appended claims.

Claims

1. An optical demultiplexer, comprising: An electro-optic modulator, when the electro-optic modulator is in a first state, changes the polarization of an optical pulse having a first polarization and passing through the electro-optic modulator from the first polarization to a second polarization; A first reflector and a second reflector, wherein the electro-optic modulator is located in an optical track between the first reflector and the second reflector, such that a light pulse traveling in the optical track between the first reflector and the second reflector passes through the electro-optic modulator, wherein the first reflector and the second reflector are located in the optical demultiplexer, such that a light pulse traveling in the optical track between the first reflector and the second reflector, during each round of travel between the first reflector and the second reflector, is shifted between the first reflector and the second reflector perpendicular to the propagation direction of the light pulse; and A first polarization beam splitter is located in the optical track between the first reflector and the electro-optic modulator, wherein the first polarization beam splitter is used for: Transmit a light pulse having the first polarization, and Reflecting a light pulse with the second polarization to remove the light pulse with the second polarization from the optical track between the first mirror and the second mirror, wherein the first polarization beam splitter is used to reflect light pulses that are shifted relative to each other perpendicular to the propagation direction onto different, respective output tracks; A third reflecting mirror is positioned at the end of the optical trajectory with normal incidence relative to the end of the optical trajectory, such that the reflected light pulse travels in opposite directions between the first reflecting mirror and the second reflecting mirror.

2. The photolysis multiplexer of claim 1, wherein, The device further includes a second polarization beamsplitter located in the optical track between the second mirror and the electro-optic modulator, wherein the second polarization beamsplitter is used for: Transmit a light pulse having the first polarization, and The second polarization light pulse is reflected to remove the second polarization light pulse from the optical track between the first and second mirrors, wherein the second polarization beam splitter is used to reflect the light pulses that are shifted relative to each other perpendicular to the propagation direction onto different, respective output tracks.

3. The photolysis multiplexer of claim 2, wherein, The device further includes a first converging lens located in an optical path between the electro-optic modulator and the first polarizing beamsplitter, wherein the first converging lens is used to converge light pulses traveling in the optical path from the electro-optic modulator to the first converging lens, such that light pulses displaced relative to each other perpendicular to the propagation direction travel parallel to each other between the first converging lens and the first polarizing beamsplitter.

4. The photolysis multiplexer of claim 3, wherein, The device further includes a second converging lens located in an optical path between the electro-optic modulator and the second mirror, wherein the second converging lens is used to converge light pulses traveling in the optical path from the electro-optic modulator to the second converging lens, such that light pulses displaced relative to each other perpendicular to the propagation direction travel parallel to each other between the second converging lens and the second mirror.

5. The photolysis multiplexer of claim 4, wherein, The second converging lens is located in an optical track between the electro-optic modulator and the second polarizing beam splitter, wherein the second converging lens is used to converge light pulses traveling in the optical track from the electro-optic modulator to the second converging lens, such that light pulses displaced relative to each other perpendicular to the propagation direction travel parallel to each other between the second converging lens and the second polarizing beam splitter.

6. The photolysis multiplexer of claim 4, wherein, The first converging lens and the second converging lens are located in the optical demultiplexer in a telescope configuration with unity magnification.

7. The photolysis multiplexer of claim 6, wherein, This causes the light pulse traveling in the optical path between the first and second mirrors to enter the input path of the optical demultiplexer, align parallel to the central axis of the telescope structure, and shift from the central axis of the telescope structure.

8. The photolysis multiplexer of claim 6, wherein, The electro-optic modulator is located at the center or central region of the telescope structure.

9. The photolysis multiplexer of claim 4, wherein, The first reflector includes a first reflector assembly and a second reflector assembly for reflecting light pulses traveling in an optical path from the first converging lens to the first reflector, wherein the first reflector assembly and the second reflector assembly are aligned perpendicularly or substantially perpendicularly to each other, and wherein the first reflector assembly and the second reflector assembly are aligned at an angle of 45 degrees or approximately 45 degrees relative to an optical path, the light pulses traveling parallel to each other on the optical path between the first converging lens and the first reflector.

10. The photolysis multiplexer of claim 9, wherein, The second reflector includes a third reflector assembly and a fourth reflector assembly for reflecting light pulses traveling in an optical path from the second converging lens to the second reflector, wherein the third reflector assembly and the fourth reflector assembly are aligned perpendicularly or substantially perpendicularly to each other, and wherein the third reflector assembly and the fourth reflector assembly are aligned at an angle of 45 degrees or approximately 45 degrees relative to an optical path, the light pulses traveling parallel to each other on the optical path between the second converging lens and the second reflector.

11. The photolysis multiplexer according to any one of claims 1 to 10, wherein, One or both of the first and second reflectors include an opening that allows light pulses to be provided into an optical path between the first and second reflectors.

12. The optical demultiplexer according to any one of claims 1 to 10, characterized in that, When the electro-optic modulator switches from the second state to the first state, the first polarization beam splitter removes light pulses with different time modes and the same spatial mode from the optical trajectory to different spatial modes. In the second state, the polarization of the light pulse with the first polarization does not change when the light pulse passes through the electro-optic modulator.

13. The optical demultiplexer according to claim 12, characterized in that, Based on the fact that all optical pulses traveling on the optical track between the first and second mirrors have the first polarization, and based on the fact that the electro-optic modulator switches from the second state to the first state such that when all optical pulses travel through the electro-optic modulator in the first state, the polarization of all optical pulses changes from the first polarization to the second polarization, the first polarization beam splitter is used to remove all optical pulses from the optical track between the first and second mirrors simultaneously or within less than 10 nanoseconds.

14. The optical demultiplexer according to claim 13, characterized in that, When the electro-optic modulator switches from the second state to the first state, the first polarization beam splitter is used to remove all optical pulses from the optical track between the first mirror and the second mirror simultaneously or within less than 10 nanoseconds, wherein each of the output tracks contains a single optical pulse from the optical pulses.

15. The optical demultiplexer according to any one of claims 1 to 9, characterized in that, The electro-optic modulator includes a Pockels unit, wherein the first state is related to the state in which the Pockels unit is turned on.

16. The optical demultiplexer according to claim 12, characterized in that, The electro-optic modulator is capable of switching between a first state and a second state in less than 10 nanoseconds. In the first state, the polarization of a light pulse with the first polarization changes as the light pulse passes through the electro-optic modulator, and in the second state, the polarization of a light pulse with the first polarization does not change as the light pulse passes through the electro-optic modulator.

17. The optical demultiplexer according to any one of claims 1 to 9, characterized in that, It further includes a set of additional reflectors located in the optical track to confine the optical track to an area of ​​1.5 meters or less by 0.5 meters or less for an optical track length of at least 6 meters.

18. A quantum computing system, characterized in that, Includes the optical demultiplexer according to any one of claims 1 to 17.

19. A quantum computing system, characterized in that, include: The optical demultiplexer according to any one of claims 1 to 17; A single-photon source is used to generate a single-photon stream, wherein the single-photon source is coupled to the optical demultiplexer to provide the single-photon stream to the optical demultiplexer. The optical demultiplexer is used to output multiple indistinguishable single photons to corresponding output trajectories in different output trajectories.

20. A method for correspondingly outputting multiple single photons onto corresponding output trajectories in different output trajectories, characterized in that, The method includes: Provide the system according to claim 19; Through the single photon source, a plurality of light pulses having a first polarization are provided into the optical track between the first and second mirrors in a manner that is aligned parallel to and shifted from the central axis of the optical track between the first and second mirrors; Switching the electro-optic modulator from a second state to a first state, wherein in the second state, the polarization of a light pulse having the first polarization does not change as the light pulse passes through the electro-optic modulator, and in the first state, the polarization of the light pulse changes from the first polarization to the second polarization; and Based on the reflection of the light pulse with the second polarization by the first polarization beam splitter, multiple single photons are correspondingly output onto different output trajectories to remove the light pulse from the optical trajectory between the first and second mirrors.

21. The method according to claim 20, characterized in that, One or more of the optical pulses travel back and forth multiple times between the first reflector and the second reflector, wherein the electro-optic modulator switches from the second state to the first state, while one of the optical pulses travels with its last round of back and forth travel between the first reflector and the second reflector.

22. The method according to claim 20 or 21, characterized in that, The beam width of the light pulse provided by the single photon source is 2 mm.

23. An optical method, characterized in that, For performing quantum computing based on (i) light pulses or (ii) multiple single photons, the light pulses being reflected onto different output trajectories using an optical demultiplexer according to any one of claims 1 to 17 or a quantum computing system according to claim 18, the multiple single photons being correspondingly output onto corresponding output trajectories in the different output trajectories using a system according to claim 19.

24. A computer-readable storage medium storing a computer program that, when executed on one or more computing devices, performs the method according to claim 23.

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