Systems and methods for single photon sources

Abstract

A system includes a quantum dot configured to generate photons. The system further includes a curved coupler optically coupled to the quantum dot. The curved coupler is configured to receive the photons from the quantum dot and separate the photons according to a curvature of the curved coupler and polarization states of the photons. The system additionally includes a waveguide configured to receive at least a portion of the separated photons of different polarization states from the curved coupler and output a signal containing quantum information from the separated photons.

Description

SYSTEMS AND METHODS FOR SINGLE PHOTON SOURCESCROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Application Number 63 / 617,009, filed January 2, 2024, entitled “SYSTEMS AND METHODS FOR SINGLE PHOTON SOURCES,” which is incorporated herein by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under Grant No. 68335-20-C- 0420 awarded by the United States Navy, Grant No. ECCS-0925532 awarded by the National Science Foundation, and Grant No. N00014-1310465 awarded by the Office of Naval Research. The government has certain rights in the invention.TECHNICAL FIELD

[0003] This disclosure relates to single photon sources, particularly to generating and / or transmitting photons.BACKGROUND

[0004] There is a need for single photon sources with improved efficiency and reduced loss.SUMMARY

[0005] The present disclosure relates to techniques for single photon sources. According to the present disclosure, photons can be generated, selectively separated, and transmitted to output a signal containing quantum information with improved efficiency and reduced loss.

[0006] One aspect of the present disclosure relates to a system. The system includes a quantum dot configured to generate photons, a curved coupler optically coupled to the quantum dot, the curved coupler being configured to receive the photons from the quantum dot and separate the photons according to a curvature of the curved coupler and polarization states of the photons, and a waveguide configured to receive at least a portion of the separated photons ofdifferent polarization states from the curved coupler and output a signal containing quantum information from the separated photons.

[0007] In some embodiments, the quantum dot is isolated within a nanostructure configured to electrically drive the quantum dot to generate the photons.

[0008] In some embodiments, the quantum dot and the curved coupler are optically coupled through a surface plasmon. In some embodiments, the curvature of the curved coupler induces an orbital angular momentum that matches a spin angular momentum of the surface plasmon in the curved coupler.

[0009] In some embodiments, a coupling distance between the quantum dot and the curved coupler ranges from about 0.1 nm to about 150 nm.

[0010] In some embodiments, an optical path of the curved coupler is shorter than an optical path of the waveguide.

[0011] In some embodiments, the signal includes a qubit.

[0012] In some embodiments, the system includes a band-pass filter coupled to the waveguide and configured to filter the at least a portion of the separated photons into the signal.

[0013] Another aspect of the present disclosure relates to a device. The device includes an emitter configured to generate polarization-entangled photons, a waveguide, a coupling structure configured to optically couple the emitter and the waveguide. The coupling structure includes a curved portion optically coupled to the emitter and configured to receive photons of different polarization states from the emitter and separate the photons depending on the polarization states of the photons, and a branch optically coupled to the waveguide and configured to transmit a separated portion of the polarization-entangled photons to the waveguide, wherein the branch is shorter in length than the waveguide. In at least one embodiment, the coupling structure includes a curved portion optically coupled to the emitter and configured to receive photons of different polarization states from the emitter and separate them into different branches depending on their respective polarizations. Each branch can be optically coupled to a corresponding waveguide and configured to transmit the separated photons thereto.

[0014] In some embodiments, the curved portion is configured to separate photons of different polarization states according to an angular momentum matching of an orbital angular momentum induced by a curvature of the curved portion and a spin angular momentum of surface plasmons on the coupling structure.

[0015] In some embodiments, the curved portion is positioned in a deep-near field region of the emitter for a near-field-trapped energy flux to be extracted out of the emitter to increase a photon emission rate and compensate for an overall insertion loss of the system.

[0016] In some embodiments, the curved portion is configured to separate the entangled photons into a first photon having a first polarization state and a second photon having a second polarization state. In some embodiments, the first polarization state is a circular polarization state in a first direction, and the second polarization state is a circular polarization state in a second direction opposite to the first direction.

[0017] In some embodiments, the polarization-separated photons are converted from a surface plasmon in the branch to an electromagnetic wave in the waveguide.

[0018] Another aspect of the present disclosure relates to a chip. The chip includes a photon emitter, electrically driven to generate photons, a first waveguide and a second waveguide, a coupler configured to receive the photons from the photon emitter. The coupler includes a first branch arranged in parallel to the first waveguide, the first branch configured to receive and transmit a first photon of the photons to the first waveguide, and a second branch arranged in parallel to the second waveguide, the second branch configured to receive and transmit a second photon of the photons to the second waveguide, a first optical filter coupled to the first waveguide, the first optical filter configured to receive the first photon from the first waveguide and output a first filtered signal containing first quantum information from the first photon, and a second optical filter coupled to the second waveguide, the second optical filter configured to receive the second photon from the second waveguide and output a second filtered signal containing second quantum information from the second photon.

[0019] In some embodiments, the photon emitter, the first waveguide, the coupler, the first optical filter, and the second optical filter are integrated within a substrate.

[0020] In some embodiments, the photons are of different polarization states. There may be no correlations among their polarization states.

[0021] In some embodiments, the photons are a polarization-entangled pair including the first photon having a first polarization state and the second photon having a second polarization state.

[0022] In some embodiments, the first branch and the first waveguide are spaced by a first distance and are coextensive for a second distance, wherein the second distance is less than about 700 nm.

[0023] In some embodiments, the chip includes an electrical interface to electrically drive the photon emitter to generate the photons, the electrical interface including at least a first electrode and at least a second electrode configured to independently control carrier energy levels associated with the photons generated by the photon emitter.

[0024] In some embodiments, the coupler includes a curved portion configured to optically connect the first branch and the second branch, wherein the photon emitter is located between the first branch and the second branch.

[0025] In some embodiments, the first photon in the first branch has a first polarization state, and the second photon in the second branch has a second polarization state different from the first polarization state.

[0026] In some embodiments, the first filtered signal includes a first qubit encoded according to the first polarization state, and the second filtered signal includes a second qubit encoded according to the second polarization state.

[0027] Both the foregoing summary and the following description of the drawings and detailed description are exemplary and explanatory. They are intended to provide further details but are not to be construed as limiting. Other objects, advantages, and novel features will be readily apparent to those skilled in the art from the following detailed description.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Aspects of the present disclosure can be understood from the following detailed description when read with the accompanying figures. It should be noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

[0029] FIG. 1 illustrates a block diagram of an example system for a single photon source, in accordance with some embodiments.

[0030] FIG. 2 illustrates a schematic diagram of an example system for a single photon source, in accordance with some embodiments.

[0031] FIG. 3A and FIG. 3B illustrate a schematic diagram of a portion of the system shown in FIG. 2, in accordance with some embodiments.

[0032] FIG. 4A and FIG. 4B illustrate a schematic diagram of an example system for a single photon source, in accordance with some embodiments.

[0033] FIG. 5A illustrates a schematic diagram of an example system for a single photon source, in accordance with some embodiments.

[0034] FIG. 5B illustrates a schematic diagram of a representation of the signals shown in FIG. 5A and corresponding quantum states, in accordance with some embodiments.

[0035] FIGS. 6A-6K illustrate schematic diagrams of spin and Poynting vector distributions associated with an example system for a single photon source, in accordance with some embodiments.

[0036] FIGS. 7A-7E plot magnetic field profiles associated with example systems for a single photon source, in accordance with some embodiments.

[0037] FIG. 8A and FIG. 8B illustrate a schematic diagram of an example system for a single photon source, in accordance with some embodiments.

[0038] FIGS. 8C-8F plot electric field profiles associated with the system shown in FIG. 8A, in accordance with some embodiments.

[0039] FIG. 9 illustrates a flow chart of an example method for a single photon source, in accordance with some embodiments.DETAILED DESCRIPTION

[0040] A single photon source (SPS) can generate and transmit photons through various optical components to output a signal containing quantum information. However, in the SPS, challenges can arise due to coupling loss and efficiency issues. In transmitting photons, the coupling loss can occur when generated photons are not efficiently transmitted through optical components, thereby diminishing signal strength of the SPS and reducing the overall throughput and transmission rate of the SPS output signals.

[0041] The present disclosure is directed to techniques for SPSs with improved emission / transmission efficiency, enhanced transmission rates of the SPS output signals, and reduced loss. Photons (e.g., entangled photons) can be transmitted through a coupler configured to receive the photons from a photon emitter and separate the photons into a first photon and a second photon according to a curved structure of the coupler. The separated photon (e.g., the first photon) can be transmitted to a waveguide configured to receive the first photon and output a signal containing quantum information associated with the first photon. In some embodiments, the photon emitter can be electrically driven to generate the entangled photons. In some embodiments, the coupler can separate the photons depending on polarization states of the photons.

[0042] The coupler may be a chiral coupler configured to extract a near-field energy flux circling around the photon emitter (e.g., a quantum dot dipole emitter). This near-field-trapped energy flux at a distance of about 1 nm can surpass a far-field radiating energy flux by about 8x 103or about 8x 104times. It should be noted that typical far-field coupling methods can access or extract only this small radiating energy flux. See Shi and Kim, “Spin texture and chiral coupling of circularly polarized dipole field,” Nanophotonics 2023; 12(1): 129-138. Extracting the near-field-trapped energy flux out of the emitter can enhance the photon emission rate. For example, about 1 % of the flux at about 1 nm distance can result in enhancing the photon emission rate by about 1000 times.

[0043] A curvature (or a radius) of the coupler can be configured (e.g., designed, arranged, etc.) such that the curvature can induce an orbital angular momentum that matches a spin angular momentum of surface plasmons in the coupler and of the dipole near-field. Through this near-field and plasmonic coupling, the coupler can improve a polarization selectivity, coupling efficiency, and output of photon signals. Consequently, the extraction (out-coupling) ofthe near-field photon flux can increase the emission rate of output photons (e.g., the overall throughput of the SPS). This deep-near-field chiral coupling can be utilized as a means of compensating the insertion losses that may occur in an integrated photonic circuit configuration of the SPS or even overcompensating (e.g., negative insertion losses).

[0044] The techniques disclosed herein can include placing an isolated photon emitter (e g., a quantum dot) inside a nanostructure (e.g., a nanohole) formed at a p-n junction. This allows the photon emitter to be electrically driven through low-voltage emission of 2- dimensional electron gas (2DEG), thereby enabling high efficiencies of carrier injection and photon emission at a low bias voltage. Furthermore, the electron and hole injection levels can be independently controlled, which allows for resonant injection of the carriers to proper energy levels of the photon emitter.

[0045] The coupler and the waveguide can be optically coupled such that the photons can be transmitted with reduced insertion loss (e.g., coupling and propagation losses, etc.). In some embodiments, the coupler and the waveguide can be coextensive for a certain distance, for the surface plasmons in the coupler to be transmitted to the waveguide with improved efficiency (e.g., about 60 %). In order to further reduce the insertion loss, the waveguide can be designed such that the loss within the coupler is reduced. For example, the length of the coupler can be shorter (e.g., a minimum length for the chiral coupling) than that of the waveguide to reduce or minimize the loss within the coupler.

[0046] The techniques disclosed herein can include various components to operate the SPS. In some embodiments, the waveguide can be optically coupled to an optical filter (e.g., a wavelength-tunable bandpass filter) to spectrally filter the photon (and / or the signal). The filtering wavelength can be tuned to desired ranges by integrating a transducer device (e.g., electro-optic, thermo-optic, etc.). In some embodiments, the techniques disclosed herein can be integrated within a circuit or a chip configured to transform the photons to path-entangled photons, and then to signals containing quantum information (e.g., through the coupler, the waveguide, the filter, etc.).

[0047] The techniques disclosed herein can reduce loss (e.g., insertion loss) in SPSs and increase coupling efficiency, thereby improving throughput (e.g., improved bit-rate) of the SPSs, while allowing for improved selectivity (e g., a polarization-selectivity) in separating entangledphotons. This can provide improved techniques in various fields, including single photon optics and quantum information processing (e.g., quantum communication, computing, sensing / metrology, etc.).

[0048] The techniques disclosed herein can include integrating the coupler, the waveguide, etc. as discussed above into a chip. The amplification effects gained from the coupler (e g., deep-near-field coupling) and / or the waveguide can compensate insertion loss of the entire chip, thereby providing a net gain. This allows for increased bit rate and improved polarization selectivity, as noted above, and enhanced emission of entangled photons with a reduced form factor (e.g., chip scale), which further can enable improved scalability of such a chip-scale circuit.

[0049] FIG. 1 illustrates a block diagram of an example system 100 for a single photon source, in accordance with some embodiments. The system 100 may be or include a device, a chip, a circuit, or any combination thereof, or any system configured to generate and transmit photons. In some embodiments, the system 100 can serve as a SPS. The system 100 includes a photon emitter 120, a coupler 140, and a waveguide 160. For example, the system 100 may be a chip or a substrate on which the photon emitter 120, the coupler 140, and the waveguide 160 are integrated.

[0050] The photon emitter 120 may be or include a nanostructure, a semiconductor nanocrystal, or any photon emitter configured to generate photons. For example, the photon emitter 120 may be or include a single quantum dot, a quantum dot light emitting diode (LED), a quantum dot display, an array of LEDs, etc. In some embodiments, the photon emitter 120 may be placed within an isolated area (e.g., a nanohole). In some embodiments, the photon emitter 120 can be electrically driven to generate the photons. For example, the photon emitter 120 can be electrically coupled to an electrical interface that can supply a driving voltage. In some embodiments, the photon emitter 120 can be optically driven. In some embodiments, the photon emitter 120 can generate entangled photons. For example, the photon emitter 120 can generate a pair of a first photon and a second photon entangled with the first photon. For example, the first photon may have a first polarization state (e.g., right-circular), and the second photon may have a second polarization state (e.g., left-circular). The generated photons can be transmitted to the coupler 140.

[0051] The coupler 140 may be or include a nanostructure, a curved structure, a plasmonic waveguide, or any component configured to optically couple the photon emitter 120 and the waveguide 160. For example, the coupler 140 can be optically coupled to the photon emitter 120 to receive the photons therefrom (e.g., plasmonic coupling). For example, the coupler 140 can be optically coupled to the waveguide 160 to transmit the first photon thereto (e.g., plasmon-dielectric coupling).

[0052] The coupler 140 can receive the entangled photons from the photon emitter 120 and separate the entangled photons into the first photon and the second photon. In some embodiments, the coupler 140 may be a chiral coupler to provide chiral separation (e.g., polarization-dependent separation) such that the first photon has a first polarization state (e.g., a circular polarization in a first direction), and the second photon has a second polarization state (e.g., a circular polarization in a second direction). In some embodiments, the coupler 140 may include a curved portion, and the coupler 140 can separate the entangled photons according to a curvature of the curved portion. For example, the curved portion can be configured to receive the entangled photons from the photon emitter 120 and separate the entangled photons according to an angular momentum matching of an orbital angular momentum induced by the curvature of the curved portion and a spin angular momentum of surface plasmons in the coupler 140. For example, the curvature of the coupler 140 can induce an orbital angular momentum that matches a spin angular momentum of the surface plasmon in the coupler 140. In some embodiments, the coupler 140 can separate the polarization-entangled photons into a first photon having a first polarization state and a second photon having a second polarization state. In some embodiments, there may be no correlation between the first polarization state and the second polarization state.

[0053] In some embodiments, a coupling distance between the photon emitter 120 and the coupler 140 can range from about 0.1 nm to about 150 nm. In some embodiments, the coupling distance between the photon emitter 120 and the coupler 140 can range in a deep-near- field range (e.g., smaller than about 10 nm). This allows an energy flux trapped in the near-field range to be coupled out to the coupler 140, thereby enhancing the emission rates of the photon emitter 120.

[0054] In some embodiments, the coupler 140 may include a first branch and a second branch optically coupled to the curved portion. For example, each of the first branch and thesecond branch may be a nanowire connected to the curved portion of the coupler 140. In some embodiments, the curved portion of the coupler 140 can direct the first photon into the first branch and direct the second photon into the second branch. For example, the curved portion of the coupler 140 can direct the first photon with the first polarization state into the first branch, and direct the second photon with the second polarization state into the second branch. In some embodiments, the photons (e.g., the first photon, the second photon) can be transmitted through the branches (e.g., the first branch, the second branch) in the form of a surface plasmon. The photons in the coupler 140 can be transmitted to the waveguide 160.

[0055] In some embodiments, the coupler 140 may be formed of at least one of, but not limited to, silver, other conductive metals, alloys, etc. For example, the coupler 140 may be formed of any material (e.g., any metal) for the photons to travel as a surface plasmon. For example, the coupler 140 may be a silver nanowire.

[0056] The waveguide 160 may be or include a nanostructure, a dielectric structure, a dielectric waveguide, or any component configured to optically couple to the coupler 140 to receive the photon therefrom and output a signal containing information associated with the received photon. The photons, transmitted from the photon emitter 120, through the branches (e.g., of the coupler 140) can be transmitted to the waveguide 160. For example, the first branch of the coupler 140 can be optically coupled to a first waveguide, and the second branch of the coupler 140 can be optically coupled to a second waveguide. For example, the first photon can be transmitted from the first branch to the first waveguide, and the second photon can be transmitted from the second branch to the second waveguide. In some embodiments, when transmitted from the coupler 140 to the waveguide 160, the photon can be converted from a surface plasmon in the coupler 140 to an electromagnetic wave in the waveguide 160. For example, the photons can be transmitted through the waveguide 160 as a waveguide mode of the waveguide 160.

[0057] In some embodiments, the waveguide may be formed of at least one of, but not limited to, any dielectric material (e.g., silicon oxide such as SiCh, silicon nitride such as SisN4, etc ), or a combination of dielectric materials, etc. For example, the waveguide may be formed of a SiOz cladding and a SisN4 core.

[0058] In some embodiments, the coupler 140 and the waveguide 160 can be optically coupled such that the coupler 140 (or a branch thereof) and the waveguide 160 may be spaced by a first distance and coextensive for a second distance. For example, the first branch of the coupler 140 can be arranged in parallel to the first waveguide and configured to transmit the first photon to the first waveguide, and the second branch of the coupler 140 can be arranged in parallel to the second waveguide and configured to transmit the second photon to the second waveguide.

[0059] In some embodiments, a length of the branch and / or the second distance may be less than a length of the waveguide 160. In some embodiments, the second distance may be less than 700 nm. This coupling between the coupler 140 and the waveguide 160 can provide a low- insertion loss coupling (e.g., coupling between the surface plasmons in the coupler 140 and the waveguide modes in the waveguide 160). The coextensive (and / or codirectional) arrangement of the coupler 140 and the waveguide 160 can improve coupling efficiency between the coupler 140 and the waveguide 160 (e g., by about 40% to 60%).

[0060] In some embodiments, the waveguide 160 can optically couple with various components. For example, the waveguide 160 can optically couple with an optical filter. The optical filter may be or include a band-pass filter, a wavelength tunable filter, or any optical component configured to spectrally filter photons (and / or signals) and generate an output in a certain spectral range. In some embodiments, the spectral range (e.g., wavelength) of the output (e.g., the photons, signals, etc.) can be tunable, for example by external means (e.g., electrooptic, thermos-optic, etc.).

[0061] FIG. 2 illustrates a schematic diagram of an example system 200 for a single photon source, in accordance with some embodiments. The system 200 may be substantially similar to or incorporate features of the system 100. In some embodiments, the system 200 can include a photon emitter 220, a coupler 240, and a waveguide 260, which may be substantially similar to or incorporate features of the photon emitter 120, the coupler 140, and the waveguide 160, respectively. As shown, the coupler 240 can include a curved portion 240C, a first branch 240A, and a second branch 240B. The waveguide 260 may be a pair of waveguides, including a first waveguide 260A and a second waveguide 260B. It should be noted that the system 200 shown in FIG. 2 is not intended to be limiting.

[0062] The photon emitter 220 may be located between the first branch 240A and the second branch 240B while optically coupled to the curved portion 240C. In some embodiments, the photon emitter 220 may be or include a quantum dot isolated within a nanostructure (e.g., a nanohole). For example, the photon emitter 220 may be a single quantum dot located within a nanohole.

[0063] The coupler 240 can optically couple the photon emitter 220 and the waveguide 260. The curved portion 240C can receive photons (e.g., entangled photons) from the photon emitter 220 and separate the photons according to a curvature of the curved portion 240C and polarization states of the photons, and the separated photons can be transmitted to the waveguide 260. The curved portion 240C can induce an orbital angular momentum that matches a spin angular momentum of a surface plasmon in the coupler 240. For example, the curved portion 240C can be configured to separate the photons (e.g., entangled photons) according to an angular momentum matching of the orbital angular momentum induced by the curvature of the curved portion 240C and the spin angular momentum of the surface plasmon in the coupler 240. That is, the photons generated in the photon emitter 220 can be transmitted to the coupler 240 through a plasmon.

[0064] In some embodiments, the curved portion 240C can be configured to separate the photons (e.g., entangled photons) into a first photon having a first polarization state (e.g., a circular polarization state in a first direction) and a second photon having a second polarization state (e.g., a circular polarization state in a second direction opposite to the first direction). For example, the first polarization state is a left-circular polarization (LCP) state, and the second polarization state is a right-circular polarization (RCP) state. That is, according to the curvature of the curved portion 240C, the first photon having the first polarization state and the second photon having the second polarization state can be separated, and then can be transmitted to the first waveguide 260A and the second waveguide 260B, respectively.

[0065] The waveguide 260 can receive the photons of different polarization states from the coupler 240 and output a signal containing quantum information from the photons. For example, the first waveguide 260A can receive the first photon having the first polarization state from the first branch 240A. The first photon in the first waveguide 260A can travel through the first waveguide 260A as an electromagnetic wave (e.g., a waveguide mode corresponding to thefirst waveguide 260A), and then can be output as a signal containing quantum information of the first photon. Likewise, the second waveguide 260B can receive the second photon having the second polarization state from the second branch 240B. The second photon in the second waveguide 260B can travel through the second waveguide 260B as an electromagnetic wave (e.g., a waveguide mode corresponding to the second waveguide 260B), and then can be output as a signal containing quantum information of the second photon.

[0066] The waveguide 260 and the coupler 240 can be optically coupled such that the photons in the coupler 240 can be converted from plasmons (e.g., surface plasmons) in the coupler 240 (e.g., the first branch 240A, the second branch 240B) to electromagnetic waves (e.g., waveguide modes) in the waveguide 260. In some embodiments, the coupling between the waveguide 260 and the coupler 240 may be or include a coextensive portion of the waveguide 260 and the coupler 240. For example, as shown in FIG. 2, the first branch 240 A and the first waveguide 260A may be spaced by a first distance 251, while being coextensive for a second distance 252. For example, as shown in FIG. 2, the first branch 240A and the first waveguide 260A may be arranged in parallel. In some embodiments, the first distance 251 may be less than a predetermined distance. In some embodiments, the second distance 252 may be less than about 700 nm. For example, the second distance 252 may be 500 nm. In some embodiments, an optical path within the coupler 240 (or within the first branch 240 A) may be shorter than an optical path within the waveguide 260 (or within the first waveguide 260A). In some embodiments, the first branch 240A may be shorter in length than the first waveguide 260A. While discussed referring to the first branch 240A and the first waveguide 260A, it should be understood that the second branch 240B and the second waveguide 260B can be arranged to operate in a similar manner. For example, the first branch 240A and the first waveguide 260A may be symmetrical to the second branch 240B and the second waveguide 260B. The coupling between the waveguide 260 and the coupler 240 disclosed herein can reduce insertion loss in transmitting the photons, thereby improving efficiency of the SPS system.

[0067] FIG. 3A and FIG. 3B illustrate a schematic diagram of a portion of the system 200, in accordance with some embodiments. More specifically, FIG. 3A shows an enlarged view of the photon emitter 220 and the coupler 240, and FIG. 3B shows an enlarged view of the photon emitter 220 and the curved portion 240C of the coupler 240. It should be noted that shown in FIG. 3A and FIG. 3B are not intended to be limiting.

[0068] Referring to FIG. 3 A, the coupler 240 can include the first branch 240A extending from the curved portion 240C in a first direction al, and the second branch 240B extending from the curved portion 240C in a second direction a2. For example, the curved portion 240C of the coupler 240 can be configured to optically connect the first branch 240A and the second branch 240B. In some embodiments, the first direction al and the y-axis may be oriented at an angle 01 with respect to each other, and the second direction a2 and the y-axis may be oriented at an angle 02 with respect to each other. In some embodiments, the angle 01 and the angle 02 may be identical. For example, as shown in FIG. 3A, the first direction al and the second direction a2 may be oriented at an angle 20 with respect to each other. The angle 0 shown in FIG. 3A is a non-limiting example, and may be any value. For example, the angle 0 shown in FIG. 3A may be about 30°, about 45°, about 60°, etc.

[0069] Referring to FIG. 3A and FIG. 3B, the curved portion 240C of the coupler 240 can be optically coupled with the photon emitter 220 with a coupling distance 230. In some embodiments, the coupling distance 230 may range from about 0.1 nm to about 150 nm. In some embodiments, the coupling distance 230 may be within a deep near-field regime (e.g., smaller than about 10 nm). This allows a large amount of energy flux trapped in the near-field regime to be coupled out to the coupler 240, and thus can enhance the photon emission rate of the photon emitter 220. Referring to FIG. 4B, the curved portion 240C is shown to have a width W (radial direction), a radius R, and a central angle (p. As discussed above, the curvature (and thus the radius R) of the curved portion 240C can induce an orbital angular momentum that corresponds to a spin angular momentum of a surface plasmon in the coupler 240. The orbital angular momentum can match the spin angular momentum of the surface plasmon, for example. For example, the curved portion 240C can be designed to separate the photons (e.g., entangled photons) according to an angular momentum matching of the orbital angular momentum induced by the curvature (and thus the radius R) and the spin angular momentum of the surface plasmon in the coupler 240. In some embodiments, the radius R can be determined according to the curvature that can provide a plasmonic coupling between the coupler 240 and the photon emitter 220. In some embodiments, the width W can be determined according to the waveguide modes within the waveguide 260.

[0070] FIG. 4A and FIG. 4B illustrate a schematic diagram of an example system 400 for a single photon source, in accordance with some embodiments. More specifically, FIG. 4A shows a cross sectional view of the system 400, and FIG. 4B shows a top view of a portion of the system 400. The system 400 may be substantially similar to or incorporate features of the system 100 (and / or the system 200). In some embodiments, the system 400 can include a photon emitter 420, a coupler 440, and a waveguide 460 (a pair of a first waveguide 460A and a second waveguide 460B), which may be substantially similar to or incorporate features of the photon emitter 120 (and / or the photon emitter 220), the coupler 140 (and / or the coupler 240), and the waveguide 160 (and / or the waveguide 260), respectively. As shown, the system 400 may include an electrical interface 480 and optical filters (e.g., a first filter 465A, a second filter 465B, etc.). The system 400 shown in FIG. 4A and FIG. 4B is not intended to be limiting.

[0071] As shown in FIG. 4A, in some embodiments, the system 400 may be integrated within a substrate, a chip, or an integrated circuit, or any combination thereof. For example, the photon emitter 420, the coupler 440, the waveguide 460, etc. may be integrated within a substrate 410. The substrate 410 may be or include various layers to accommodate at least one of the photon emitter 420, the coupler 440, the waveguide 460, etc. For example, as shown in FIG. 4A, the substrate 410 may include a semiconductor substrate 10 (e.g., silicon), an insulating layer 20 (e.g., silicon oxide), and a doped layer 30 (e.g., p-type silicon, n-type silicon, etc.). The substrate 410 may be or include various layers and / or structures to control at least one of the photon emitter 420, the coupler 440, the waveguide 460, etc. For example, the substrate 410 may include a semiconductor junction (e.g., a p-n junction). For example, as shown in FIG. 4A, the substrate 410 may include the electrical interface 480. The electrical interface 480 may be or include a semiconductor device or structure configured to electrically drive the photon emitter 420. It should be noted that the system 400 shown in FIG. 4A and FIG. 4B is not intended to be limiting. For example, various materials, other than those shown in FIG. 4A and FIG. 4B, can be used.

[0072] In some embodiments, the electrical interface 480 may include a first electrode 480A, a second electrode 480B, and a third electrode 480C. The electrical interface 480 can electrically drive the photon emitter 420 through the first electrode 480A, the second electrode 480B, and the third electrode 480C. For example, the first electrode 480A, the second electrode 480B, and the third electrode 480C can be utilized to independently control energy levels forinjection of carrier (e.g., electron, hole) into the photon emitter 420 (e.g., a quantum dot) such that the photon emitter 420 can be excited to generate entangled photons at certain energy states. For example, the first electrode 480A and the second electrode 480B can be utilized to independently control an energy level for injection of a hole (or an electron), while the third electrode 480C and the second electrode 480B can be utilized to independently control an energy level for injection of an electron (or a hole), thereby electrically drive the photon emitter 420 through resonant excitation of the photon emitter 420 (e.g., a quantum dot) exciton states. In some embodiments, as shown in FIG. 4A, the electrical interface 480 can control emission of the photon emitter 420 through low-voltage emission of two-dimensional electron gas (2DEG). Although depicted to include three terminals (e.g., the first electrode 480A, the second electrode 480B, and the third electrode 480C), the electrical interface 480 may be or include a two- terminal system to electrically drive the photon emitter 420.

[0073] In some embodiments, the electrical interface 480 may be, include, or coupled to a conducting structure 490 through which the photon emitter 420 is electrically driven to generate photons. For example, the conducting structure 490 may be an electrode structure formed of at least one of, but not limited to, indium tin oxide (ITO), or other conductive oxides, etc.

[0074] In some embodiments, as shown in FIG. 4B, the system 400 can include the optical filters (e g., the first filter 465 A, the second filter 465B, etc ). The optical filters may be or include a bandpass filter, a wavelength tunable filter, a ring resonator, etc. The optical filters can be optically coupled to the waveguide 460 to filter the photons (e.g., electromagnetic waves, waveguide modes, etc.) in the waveguide 460 and output a filtered signal (e.g., electromagnetic waves, waveguide modes, etc. at a filtered wavelength or wavelength range). The filtered signal can contain quantum information of the photon that has travelled a corresponding path. For example, as shown, the first filter 465A can be optically coupled to the first waveguide 460A and configured to receive the first photon from the first waveguide 460A. The first filter 465A can filter the first photon into a first filtered signal (e.g., the first photon having a filtered wavelength or wavelength range) and output the first filtered signal containing first quantum information of the first photon. Likewise, the second filter 465B can be optically coupled to the second waveguide 460B and configured to receive the second photon from the second waveguide 460B. The second filter 465B can filter the second photon into a second filtered signal (e.g., the secondphoton having a filtered wavelength or wavelength range) and output the second filtered signal containing second quantum information of the second photon. In some embodiments, the first quantum information and the second quantum information may have different information, depending on the optical path of the photon that has travelled the respective optical path.

[0075] In some embodiments, the spectral characteristics (e.g., a filtering wavelength or wavelength range, a bandwidth and / or a center wavelength for filtering, etc.) of the optical filters (e.g., the first filter 465A, the second filter 465B, etc.) can be tunable. For example, the spectral characteristics of the optical filters can be tuned (e.g., electro-optically, thermos-optically, etc.) using an external system (e.g., a transducer device).

[0076] FIG. 5A illustrates a schematic diagram of an example system 500 for a single photon source, in accordance with some embodiments. The system 500 may be substantially similar to or incorporate features of the system 100 (and / or the system 200, the system 400). In some embodiments, the system 500 can include a photon emitter 520 and optical filters (e.g., a first filter 565A, a second filter 565B, a third filter 565C, a fourth filter 565D, etc.), which may be substantially similar to or incorporate features of the photon emitter 120 (and / or the photon emitter 220, the photon emitter 420) and the optical filters (e.g., the first filter 465 A, the second filter 465B), respectively. The system 500 can include a coupling component 550, which incorporates a coupler (e.g., the coupler 140, the coupler 240, the coupler 440) and a waveguide (e.g., the waveguide 160, the waveguide 260, the waveguide 460). The system 500 can include routing waveguides (e.g., a first routing waveguide 570A, a second routing waveguide 570B, a third routing waveguide 570C, a fourth routing waveguide 570D, etc.). The system 500 shown in FIG. 5A is not intended to be limiting.

[0077] Referring to FIG. 5A, the photon emitter 520 can generate one or more photons. For example, the photon emitter 520 can generate polarization-entangled photon pairs as output photons. In some embodiments, when the photon emitter 520 generates two photons, each of which can have a first polarization and a second polarization, a combination of four different states can be output: the first photon with the first or second polarization state, and the second photon with the first or second polarization state. The photons can be coupled (e.g., transmitted) to the coupling component 550, and then transmitted to the optical filters and consequently to the routing waveguides. In some embodiments, referring to the first row of the waveguide in FIG.5 A, a first photon can be transmitted to the first filter 565A and then to the first routing waveguide 570A (a first path 571A), a second photon can be transmitted to the second filter 565B and then to the second routing waveguide 570B (a second path 57 IB), a third photon can be transmitted to the third filter 565C and then to the third routing waveguide 570C (a third path 571C), and a fourth photon can be transmitted to the fourth filter 565D and then to the fourth routing waveguide 570D (a fourth path 571D). In some embodiments, the first photon and the second photon may have a first polarization state, and the third photon and fourth photon may have a second polarization state. In some embodiments, the first polarization may be a rightcircular polarization, and the second polarization may be a left-circular polarization. In some embodiments, the first photon and the fourth photon may have a first wavelength or wavelength range, and the second photon and the third photon may have a second wavelength or wavelength range. In some embodiments, the first wavelength or wavelength range can be substantially similar to the second wavelength or wavelength range with a wavelength difference of no more than a predetermined deviation or a range of deviations.

[0078] In some embodiments, the optical filters can be tuned to filter the photons at the respective wavelengths. For example, the first filter 565A can be tuned to filter the first photon having the first wavelength or wavelength range into a first filtered signal 575 A having a first filtered wavelength or wavelength range. Likewise, the second filter 565B can be tuned to filter the second photon having the second wavelength or wavelength range into a second filtered signal 575B having a second filtered wavelength or wavelength range, the third filter 565C can be tuned to filter the third photon having the third wavelength or wavelength range into a third filtered signal 575C having a third filtered wavelength or wavelength range, and the fourth filter 565D can be tuned to filter the fourth photon having the fourth wavelength or wavelength range into a fourth filtered signal 575D having a fourth filtered wavelength or wavelength range.

[0079] The routing waveguides can receive the filtered signals from the optical filters, and then can output the same. As shown in FIG. 5A, the first routing waveguide 570A can receive and output the first filtered signal 575A (referred to as the first signal 575A, hereinafter), the second routing waveguide 570B can receive and output the second filtered signal 575B (referred to as the second signal 575B, hereinafter), the third routing waveguide 570C can receive and output the third filtered signal 575C (referred to as the third signal 575C,hereinafter), and the fourth routing waveguide 570D can receive and output the fourth filtered signal 575D (referred to as the fourth signal 575D, hereinafter).

[0080] The first signal 575A, the second signal 575B, the third signal 575C, and the fourth signal 575D can each represent a quantum state (e.g., different quantum information of the respective photon) of a photon quantum bit (qubit). In some embodiments, the first signal 575A can represent a first state of a first qubit (e.g., |R> i), the second signal 575B can represent a first state of a second qubit (e.g., |R>2), the third signal 575C can represent a second state of the second qubit (e.g., |L>2), and the fourth signal 575D can represent a second state of the first qubit (e.g., |L>i), where “R” indicates the first polarization state or the right-circular polarization (e.g., the first state), “L” indicates the second polarization state or the left-circular polarization (e g., the second state), the subscript “i” indicates the first wavelength or wavelength range (or the first filtered wavelength or wavelength range) (e.g., the first qubit), and the subscript “2” indicates the second wavelength or wavelength range (or the second filtered wavelength or wavelength range) (e.g., the second qubit).

[0081] FIG. 5B illustrates a schematic diagram of a representation 580 of the signals shown in FIG. 5A and corresponding quantum states, in accordance with some embodiments. In some embodiments, as shown, the first signal 575A and the fourth signal 575D can be defined as the first qubit |Q1 >. The first signal 575A can represent the first qubit in the first state (|0>i) (e.g., the qubit containing path-encoded information of the first path 571A), and the fourth signal 575D can represent the first qubit in the second state (| 1 >1) (e.g., the qubit containing path- encoded information of the fourth path 571D). Likewise, the second signal 575B and the third signal 575C can be defined as the second qubit |Q2> . The second signal 575B can represent the second qubit in the first state (|0>2) (e.g., the qubit containing path-encoded information of the second path 571B), and the third signal 575C can represent the second qubit in the second state (| 1 >2) (e.g., the qubit containing path-encoded information of the third path 571C). In some embodiments, a quantum superposition of the states of the first qubit and the second qubit can be represented as |00>i2 + 111 >12.

[0082] FIGS. 6A-6K illustrate schematic diagrams of spin and Poynting vector distributions 600 associated with an example system for a single photon source, in accordance with some embodiments. In some embodiments, the spin and Poynting vector distributions 600may be associated with the system 100, the system 200, the system 400, and / or the system 500. For example, the spin and Poynting vector distributions 600 may be of photons generated in the photon emitters (e.g., the photon emitter 120, the photon emitter 220, the photon emitter 420, the photon emitter 520, etc.). Thus, some of the references used above may be used in the following discussion of the spin and Poynting vector distributions 600. It should be noted that the spin and Poynting vector distributions 600 are merely an example and are not intended to limit the present disclosure.

[0083] FIG. 6A shows a spherical coordinate system in which a dipole moment p = (x + i ) is placed at the origin. That is, the dipole moment can be formed along the z-axisV2 direction. S(r, 9, (p) indicates the spin vectors of the dipole moment, and P(r, 9, <p) indicates the Poynting vectors of the dipole moment. As shown in FIGS. 6C-6E and 6G-6I, examples of the spin texture and the energy flow distribution of the dipole with circular polarizations are shown with the spin vectors and the Poynting vectors. FIG.6B shows the spin density (left) and the energy (right) as a function of a distance (e.g., r in FIG. 6A).

[0084] The angular distribution (9, (p) of the spin vectors calculated at r = 5 nm are shown in FIGS. 6C and 6D, and the corresponding Poynting vectors distribution is shown in FIG. 6E. As shown, the spin vectors can be orthogonal to the energy flow direction, indicating the traverse spins at a near field regime. FIG. 6F shows the spin vector and the Poynting vector distributions as a function of a polar angle (0). As shown, the spin can flip when scanned along the polar angle (e.g., from 0 to TI).

[0085] The angular distribution (9, (p) of the spin vectors calculated at r = 1 pm are shown in FIGS. 6G and 6H, and the corresponding Poynting vectors distribution is shown in FIG. 61. As shown, the spin vectors can be parallel (or antiparallel) to the energy flow direction, indicating the longitudinal spins at a far field regime. FIG. 6J shows the spin vector and the Poynting vector distributions as a function of a polar angle (0).

[0086] FIGS. 7A-7E plot magnetic field profiles 700 associated with example systems for a single photon source, in accordance with some embodiments. In some embodiments, the magnetic field profiles 700 may be associated with the system 100, the system 200, the system 400, and / or the system 500. For example, the magnetic field profiles 700 may be of the photons within the coupler 140, the coupler 240, the coupler 440, etc. Thus, some of the references usedabove may be used in the following discussion of the magnetic field profiles 700. It should be noted that the magnetic field profiles 700 are merely an example and are not intended to limit the present disclosure.

[0087] The magnetic field profiles 700 show the coupling (e.g., the chiral coupling) as a function of a radius of the coupler. As shown, FIGS. 7A-7E show the magnitude of the magnetic field of the photons within the coupler (e.g., the coupler 240) whose curved portion (e g., the curved portion 240C) has a radius of 15 nm, 30 nm, 54 nm, 100 nm, and 200 nm, respectively. The left panels indicate the magnetic field profiles at 1 nm below the coupler bottom surface, and the right panels indicate the field intensity after the photons propagate a waveguide distance of 1.155 pm.

[0088] In the magnetic field profiles 700, for example when the radius is 54 nm, the curvature-induced angular momentum can match the spin angular momentum of the dipole filed and the surface plasmons with improved coupling efficiency. Thus, such an exemplary system configuration (e.g., including the exemplary coupler the radius or the curvature thereof, etc.), can achieve improved chiral coupling with an increased polarization selectivity (e.g., about 100 in terms of the peak intensity) and an increased Purcell factor (e.g., about 10 in terms of the power ratio). This enhanced Purcell factor (e.g., about 10) can imply that about 10 times more photons can be extracted out of the emitter (e.g., a dipole emitter, a photon emitter, etc.) compared to a system utilizing far-field radiating photons (e.g., a dipole placed in free space) without any plasmonic coupler. This can result in about 10 times enhancement of photon emission rate, and this gain (or amplification of rates) can be utilized to compensate (or even overcompensate) insertion losses that may occur when the extracted photons travel down in integrated waveguide circuits.

[0089] FIG. 8A and FIG. 8B illustrate a schematic diagram of an example system 800 for a single photon source, in accordance with some embodiments. FIGS. 8C-8F plot electric field profiles 850 associated with the system 800, in accordance with some embodiments. In some embodiments, the system 800 may be substantially similar to or incorporate features of the system 100, the system 200, the system 400, and / or the system 500. For example, the system 800 shows a coupling between the coupler (e.g., the coupler 140, the coupler 240, the coupler 440, etc.) and the waveguide (e.g., the waveguide 160, the waveguide 260, the waveguide 460, etc.).The electric field profiles 850 may be of the coupling in the system 800. It should be noted that the system 800 and the electric field profiles 850 are merely an example and are not intended to limit the present disclosure.

[0090] FIG. 8A shows a side view of the system 800, and FIG. 8B shows a top view thereof. As shown, the system 800 includes a coupler 840 (e.g., the coupler 140, the coupler 240, the coupler 440, etc.) and a waveguide 860 (e.g., the waveguide 160, the waveguide 260, the waveguide 460, etc.). The coupler 840 can include a curved portion 840C, a first branch 840A, and a second branch 840B. The waveguide 860 can include a first waveguide 860A and a second waveguide 860B. The system 800 can include a dipole emitter (e.g., the photon emitter 120, the photon emitter 220, the photon emitter 420, etc.) (not shown). For example, the dipole emitter can be located at a distance (e.g., 3 nm) from the coupler 840.

[0091] In some embodiments, the waveguide 860 may include a silicon nitride (e.g., SiaN4) waveguide with a silicon oxide (e.g., SiCh) cladding / gap horizontally placed next to the coupler 840. For example, the waveguide 860 may be a square waveguide (e.g., 250 nm by 250 nm) with 10 nm cladding / gap. In some embodiments, as shown, the coupler 840 and the waveguide 860 can each a bent structure (e.g., a bending angle of 90°, 0 = 45° in FIG. 3A, etc.).

[0092] FIGS. 8C-8F show the electric field profiles 850. More specifically, FIG. 8C shows the intensity distribution at 5 nm above a top surface of the coupler 840 (in log scale, a top view according to FIG. 8B), and FIG. 8D shows the corresponding distribution at a middle portion of the waveguide 860 (in linear scale, a top view according to FIG. 8B). FIG. 8E shows the corresponding distribution after the photons propagate a waveguide distance of 4 pm in the first waveguide 860A (a cross sectional view according to FIG. 8A), and FIG. 8F shows the corresponding distribution after the photons propagate a waveguide distance of 4 pm in the second waveguide 860B (a cross sectional view according to FIG. 8A).

[0093] In some embodiments, as shown, a plasmonic waveguide (e g., the coupler 840) can be coextensive with and / or in parallel to a dielectric waveguide (e.g., the waveguide 860) for a certain distance. When the photons propagate this co-directional region, a power of the photons can be transferred from the plasmonic waveguide (e.g., the coupler 840) to the dielectric waveguide (e.g., the waveguide 860). While providing the chiral coupling (polarizationdependent coupling and separation, as shown in FIGS. 8C-8F), propagating the photons withinthe plasmonic waveguide may be lossy compared to propagating within the dielectric waveguide, resulting in propagation loss and thus in an insertion loss. In order to address this, the waveguide and the coupler can be configured such that the loss within the coupler is reduced. For example, the length of the coupler can be shorter (e.g., a minimum length for the chiral coupling) than that of the waveguide to reduce / minimize the loss within the coupler, allowing the photons to travel more in the dielectric waveguide. After the propagation within the coupler, the photons can be transferred to the waveguide (e.g., a low-loss dielectric waveguide). This coupler-to-waveguide design can reduce surface-plasmon propagation losses to about 3 dB or lower. This heterocoupler design can demonstrate high efficiency of coupling (e.g., about 60 %). Taking into account the high Purcell enhancement (e.g., about 10), the overall insertion loss of this integral configuration can be even negative, implying a net gain of photon emission rate.

[0094] Explanatory examples of FIGS. 6A-6K, FIGS. 7A-7E, and FIGS. 8A-8F are discussed in greater detail in Shi and Kim, “Spin texture and chiral coupling of circularly polarized dipole field,” Nanophotonics 2023; 12(1): 129-138), the entirety of which is incorporated by reference herein.

[0095] FIG. 9 illustrates a flow chart of an example method 900 for a single photon source, in accordance with some embodiments. The method 900 can be performed to output a signal containing quantum information, based on the systems disclosed herein (e.g., the system 100, the system 200, the system 400, the system 500, etc ). Thus, some of the references used above may be used in the following discussion of the method 900. It should be noted that the method 900 is merely an example and is not intended to limit the present disclosure.Accordingly, it should be understood that additional operations may be provided before, during, and after the method 900 of FIG. 9, and that certain operations may only be briefly described herein.

[0096] In a brief overview, the method 900 can start with step 910 of generating, by a photon emitter, photons. The method 900 can continue to step 920 of receiving, by a coupler, the photons. The method 900 can continue to step 930 of separating, by the coupler, the photons based on a curvature of the coupler. The method 900 can continue to step 940 of receiving, by a waveguide, a first photon of the separated photons. The method 900 can continue to step 950 of outputting a signal based on the first photon.

[0097] At step 910, a photon emitter (e.g., the photon emitter 120, the photon emitter 220, the photon emitter 420, etc.) can generate one or more photons. In some embodiments, the photon emitter can generate entangled photons. For example, the photon emitter can generate photons having entangled states (e.g., entangled polarization states). For example, the entangled polarization states may include a first circular polarization state in a first direction and a second circular polarization state in a second direction opposite to the first direction.

[0098] At step 920, a coupler can receive the photons, in response to generating (e.g., by the photon emitter) the photon at step 910. In some embodiments, the coupler can receive the entangled photons and simultaneously separate the entangled photons as discussed below at step 930. In some embodiments, the coupler can receive the photons through a plasmonic coupling between the photon emitter and the coupler. For example, the photons generated in the photon emitter can be coupled to a curved portion of the coupler as a plasmon.

[0099] At step 930, the coupler can separate the photons based on a curvature of the coupler, in response to receiving the photons at step 920. In some embodiments, the coupler can separate the photons depending on the polarization states of the photon. For example, the coupler can separate the photons into a first photon having a first polarization state (e.g., a first circular polarization in a first direction) and a second photon having a second polarization state (e.g., a second circular polarization in a second direction). In some embodiments, the coupler can separate the photons according to the curvature of the coupler. For example, the curvature can be designed such that the curvature can induce an orbital angular momentum that matches a spin angular momentum of surface plasmons in the coupler and of the dipole near-field.

[0100] At step 940, a waveguide can receive the first photon of the separated photons, in response to separating (e.g., by the coupler) the photons at step 930. In some embodiments, the waveguide can receive the first photon through a plasmonic-dielectric coupling between the coupler and the waveguide. For example, a surface plasmon of the first photon in the coupler can be transmitted to an electromagnetic wave (e.g., a waveguide mode) in the waveguide. In some embodiments, in response to receiving the first photon, at step 940, the first photon in the waveguide can be filtered (e.g., using a bandpass filter).

[0101] At step 950, the waveguide can output a signal based on the first photon, in response to receiving the first photon at step 940. The signal output from the waveguide cancontain quantum information of the first photon. For example, the signal can include path- encoded information (e.g., the polarization state of the photon).

[0102] Directional terms as used herein — for example up, above, below, down, right, left, front, back, top, bottom, vertical, horizontal — are made only with reference to the figures as drawn and are not intended to imply absolute orientation unless otherwise expressly stated.

[0103] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification.

[0104] As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise. Also, the word “or” when used without a preceding “either” (or other similar language indicating that “or” is unequivocally meant to be exclusive - e.g., only one of x or y, etc.) shall be interpreted to be inclusive (e.g., “x or y” means one or both x or y).

[0105] The term “and / or” shall also be interpreted to be inclusive (e.g., “x and / or y” means one or both x or y). In situations where “and / or” or “or” are used as a conjunction for a group of three or more items, the group should be interpreted to include one item alone, all the items together, or any combination or number of the items. Moreover, terms used in the specification and claims such as have, having, include, and including should be construed to be synonymous with the terms comprise and comprising. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. As a non-limiting example, a reference to “Xand / or Y” may refer, in one embodiment, to X only (optionally including elements other than Y); in some embodiments, to Y only (optionally including elements other than X); in yet some embodiments, to both X and Y (optionally including other elements).

[0106] The drawings may be interpreted, for example, as showing: (a) everything drawn to scale, (b) nothing drawn to scale, or (c) one or more features drawn to scale and one or more features not drawn to scale. Accordingly, the drawings may serve to provide support to recite the sizes, proportions, and / or other dimensions of any of the illustrated features either alone or relative to each other. Furthermore, all such sizes, proportions, and / or other dimensions are to be understood as being variable from 0-100% in either direction and thus provide support for claims that recite such values or any and all ranges or subranges that may be formed by such values.

[0107] References to specific examples, use of “i.e.,” use of the word “invention,” etc., are not meant to invoke exception (b) or otherwise restrict the scope of the recited claim terms. Other than situations where exception (b) applies, nothing contained in this document should be considered a disclaimer or disavowal of claim scope.

[0108] Unless the context indicates otherwise, it is specifically intended that the various features of the disclosure described herein may be used in any combination. Moreover, the disclosure also contemplates that in some embodiments, any feature or combination of features set forth herein may be excluded or omitted. To illustrate, if the specification states that a device comprises components A, B and C, any of A, B or C, or a combination thereof, may be omitted and disclaimed singularly or in any combination.

[0109] As used herein, “about” or “approximately” will be understood by persons of ordinary skill in the art and will vary to some extent depending upon the context in which it is used. If there are uses of the term which are not clear to persons of ordinary skill in the art, given the context in which it is used, “about” or “approximately” will mean up to plus or minus 10% of the particular term.

[0110] While certain embodiments have been illustrated and described, it should be understood that changes and modifications may be made therein in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the following claims.

[0111] The embodiments, illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms “comprising,” “including,” “containing,” etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claimed technology. Additionally, the phrase “consisting essentially of’ will be understood to include those elements specifically recited and those additional elements that do not materially affect the basic and novel characteristics of the claimed technology. The phrase “consisting of’ excludes any element not specified.

[0112] The present disclosure is not to be limited in terms of the particular embodiments described in this application. Many modifications and variations may be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and compositions within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, which may of course vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0113] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof, inclusive of the endpoints. As such, all disclosed ranges are to be understood to encompass and provide support for claims that recite any and all subranges or any and all individual values subsumed by each range. For example, a stated range of 1 to 10 should be considered to include and provide support for claims that recite any and all subranges or individual values that are between and / or inclusive of the minimum value of 1 and the maximum value of 10; that is, all subrangesbeginning with a minimum value of 1 or more and ending with a maximum value of 10 or less (e g., 5.5 to 10, 2.34 to 3.56, and so forth) or any values from 1 to 10 (e.g., 3, 5.8, 9.9994, and so forth).

[0114] Any listed range may be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein may be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like, include the number recited and refer to ranges which may be subsequently broken down into subranges as discussed above. Further, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 layers refers to groups having 1, 2, or 3 layers. Similarly, a group having 1-5 layers refers to groups having 1, 2, 3, 4, or 5 layers, and so forth.

[0115] Any publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.

[0116] Other embodiments are set forth in the following claims.

Claims

WHAT IS CLAIMED SIS:

1. A system comprising: a quantum dot configured to generate photons; a curved coupler optically coupled to the quantum dot, the curved coupler configured to receive the photons from the quantum dot and separate the photons according to a curvature of the curved coupler and polarization states of the photons; and a waveguide configured to receive at least a portion of the separated photons of different polarization states from the curved coupler and output a signal containing quantum information from the separated photons.

2. The system of claim 1, wherein the quantum dot is isolated within a nanostructure configured to electrically drive the quantum dot to generate the photons.

3. The system of claim 1, wherein the quantum dot and the curved coupler are optically coupled through a surface plasmon.

4. The system of claim 3, wherein the curvature of the curved coupler induces an orbital angular momentum that matches a spin angular momentum of the surface plasmon in the curved coupler.

5. The system of claim 1, wherein a coupling distance between the quantum dot and the curved coupler ranges from about 0.1 nm to about 150 nm.

6. The system of claim 1, wherein an optical path of the curved coupler is shorter than an optical path of the waveguide.

7. The system of claim 1, wherein the signal includes a qubit.

8. The system of claim 1, further comprising a band-pass filter coupled to the waveguide and configured to filter the at least a portion of the separated photons into the signal.

9. A device comprising: an emitter configured to generate polarization-entangled photons; a waveguide; a coupling structure configured to optically couple the emitter and the waveguide, the coupling structure comprising: a curved portion optically coupled to the emitter and configured to receive the photons of different polarization states from the emitter and separate the photons depending on the polarization states of the photons; and a branch optically coupled to the waveguide and configured to transmit a separated portion of the polarization-entangled photons to the waveguide, wherein the branch is shorter in length than the waveguide.

10. The system of claim 9, wherein the curved portion is configured to separate the photons of different polarization states according to an angular momentum matching of an orbital angular momentum induced by a curvature of the curved portion and a spin angular momentum of surface plasmons in the coupling structure.

11. The system of claim 9, wherein the curved portion is positioned in a deep-near-field region of the emitter for a near-field-trapped energy flux to be extracted out of the emitter to increase a photon emission rate and compensate an overall insertion loss of the system.

12. The device of claim 9, wherein the curved portion is configured to separate the polarization-entangled photons into a first photon having a first polarization state and a second photon having a second polarization state.

13. The device of claim 12, wherein the first polarization state is a circular polarization state in a first direction, and the second polarization state is a circular polarization state in a second direction opposite to the first direction.

14. The device of claim 9, wherein the polarization-separated photons are converted from a surface plasmon in the branch to an electromagnetic wave in the waveguide.

15. A chip comprising: a photon emitter, electrically driven to generate photons; a first waveguide and a second waveguide; a coupler configured to receive the photons from the photon emitter, the coupler comprising: a first branch arranged in parallel to the first waveguide, the first branch configured to receive and transmit a first photon of the photons to the first waveguide; and a second branch arranged in parallel to the second waveguide, the second branch configured to receive and transmit a second photon of the photons to the second waveguide; a first optical filter coupled to the first waveguide, the first optical filter configured to receive the first photon from the first waveguide and output a first filtered signal containing first quantum information from the first photon; and a second optical filter coupled to the second waveguide, the second optical filter configured to receive the second photon from the second waveguide and output a second filtered signal containing second quantum information from the second photon.

16. The chip of claim 15, wherein the photon emitter, the first waveguide, the coupler, the first optical filter, and the second optical filter are integrated within a substrate.

17. The chip of claim 15, wherein the photons are a polarization-entangled pair comprising the first photon having a first polarization state and the second photon having a second polarization state.

18. The chip of claim 15, wherein the first branch and the first waveguide are spaced by a first distance and are coextensive for a second distance, wherein the second distance is less than about 700 nm.

19. The chip of claim 15, comprising an electrical interface to electrically drive the photon emitter to generate the photons, the electrical interface comprising at least a first electrode and at least a second electrode configured to independently control carrier energy levels associated with the photons generated by the photon emitter.

20. The chip of claim 15, comprising a curved portion of the coupler, the curved portion configured to optically connect the first branch and the second branch, wherein the photon emitter is located between the first branch and the second branch.

21. The chip of claim 15, wherein the first photon in the first branch has a first polarization state, and the second photon in the second branch has a second polarization state different from the first polarization state.

22. The chip of claim 21, wherein the first filtered signal includes a first qubit encoded according to the first polarization state, and the second filtered signal includes a second qubit encoded according to the second polarization state.

Images