Light source, system and method for photonic sampling

Abstract

The invention relates to a light source (10) for an optical quantum system (20) for photonic sampling, wherein the light source (10) comprises: - a waveguide-based two-mode squeezer (12), configured to generate squeezed optical quantum states (12a) from a single physical light source (26); - a polarization control element, comprising at least one polarization manipulation element (14) arranged in an optical path of the generated optical quantum states of the two-mode squeezer (12); and - a polarization-dependent beam splitter (16), arranged in an optical path of an output of the polarization control element, and configured to separate or combine polarization components depending on a setting of the polarization manipulation element (14) of the polarization control element. Furthermore, the invention relates to an optical quantum system (20) comprising the above light source (10), and to a method for performing photonic sampling experiments, preferably with said optical quantum system (20).

Description

[0001] UNIVERSIT AT PADERBORN Dusseldorf, 16 September 2025

[0002] Our Reference: UD 42256 / SAM

[0003] Universitat Paderborn

[0004] Warburger Str. 100, 33098 Paderborn, Germany

[0005] Light source, system and method for photonic sampling

[0006] D e s c r i p t i o n

[0007] The present invention relates to a light source for an optical quantum system for photonic sampling.

[0008] Furthermore, the invention relates to an optical quantum system comprising such a light source, as well as to a method for performing photonic sampling experiments preferably using said source.

[0009] Boson Sampling is a quantum optical computational model that serves as a key candidate for demonstrating quantum advantage. It enables the execution of classically intractable sampling tasks using linear optical networks and quantum light sources. Depending on the choice of input states, different variants of Boson Sampling can be implemented — most notably, Fock State Boson Sampling, which requires single photons from two-mode squeezed sources, and Gaussian Boson Sampling, which is performed using single-mode squeezed vacuum states.

[0010] Conventionally, photonic experiments are designed and optimized for one specific sampling regime. As a result, experimental platforms typically rely on light sources that are tailored either to generate single-mode squeezed states for Gaussian Boson Sampling or to generate two-mode entangled photon pairs for Fock State Boson Sampling. This specialization, however, imposes major limitations, as two separate hardware setups are required to explore the two sampling regimes and it is not possible to flexibly switch between single-mode and two-mode squeezing within the same source module.

[0011] This lack of tunability increases experimental complexity, footprint, and cost. It also restricts the ability to directly compare or transition between Gaussian and Fock-state Boson Sampling within the same interferometric and detection infrastructure. Moreover, there the exploration of intermediate regimes between pure single-mode and pure two-mode squeezing, which may prove useful in probing hybrid computational models or for error interpolation studies is not possible.

[0012] Accordingly, there exists a need for exploring dynamic switching between different squeezing regimes.

[0013] It is an object to provide means which overcomes at least one disadvantage of the prior art solutions. Preferably, it is an object of the invention to provide means to switch between Fock state Boson sampling and Gaussian boson sampling and to investigate the operating regime between Fock state Boson sampling and Gaussian boson sampling.

[0014] The object is solved by the features of the independent claims. Preferred implementations are described in the dependent claims.

[0015] Thus, the object is solved by a light source for an optical quantum system for photonic sampling, wherein the light source comprises: a waveguide-based two-mode squeezer, configured to generate squeezed optical quantum states from a single physical light source; a polarization control element, comprising at least one polarization manipulation element arranged in an optical path of the generated optical quantum states of the two-mode squeezer; and a polarization-dependent beam splitter, arranged in an optical path of an output of the polarization control element, and configured to separate or combine polarization components depending on a setting of the polarization manipulation element of the polarization control element.

[0016] Furthermore, the object is solved by an optical quantum system for photonic sampling, wherein the system is configured to generate squeezed quantum states in the time domain and to interfere the quantum states in the spatial domain, the system comprising:

[0017] (a) a light source being configured as described above,

[0018] (b) a conversion element configured to map the temporally generated optical quantum states into spatially separated optical quantum states; and

[0019] (c) a spatially implemented linear optical network, configured to interfere the spatial separated optical quantum states.

[0020] Additionally, a method for performing photonic sampling experiments is provided, the method preferably performed with the above optical quantum system, comprising the step:

[0021] - generating a sequence of squeezed optical quantum states in the time domain, and

[0022] - defining a degree of squeezing between two-mode squeezing and single-mode squeezing of the generated optical quantum states by adjusting a polarization manipulation element of a polarization control element.

[0023] A common feature of experimental platforms known in prior art is that they typically rely on light sources that are tailored either to generate single-mode squeezed states for Gaussian Boson Sampling or to generate two-mode entangled photon pairs for Fock State Boson Sampling. An aspect of the invention is, that the light source is designed to flexibly generate squeezed optical quantum states suitable for various Boson Sampling protocols, including both Gaussian and Fock-state regimes. The light source comprises the waveguide-based two-mode squeezer, which is configured to generate squeezed optical quantum states from a single physical light source. In contrast to bulk optical systems, the use of waveguide technology enables compact integration, reduced optical losses, and high coupling efficiency. The two-mode squeezer is designed to generate photon pairs in well-defined polarization modes, which form the basis for both two-mode and single-mode squeezed outputs depending on downstream polarization control. Parametric down-conversion, typically in a nonlinear medium such as a PPKTP waveguide, efficiently converts photons of the single physical light source into pairs of correlated photons exhibiting squeezing.

[0024] The polarization control element is arranged in the optical path of the generated quantum states. This element comprises of at least one polarization manipulation element, such as a half-wave plate or an electro optical modulator, which enables dynamic adjustment of the polarization basis of the output modes. This allows the operator to manipulate how the squeezed modes interact make it possible to switch between two-mode and single-mode output regimes.

[0025] Downstream of the polarization control element, the polarization-dependent beam splitter is arranged. This beam splitter is configured to either separate or interfere the polarization components of the generated quantum states, depending on the setting of the polarization manipulation element.

[0026] Thus, the light source supports multiple operation regimes: When the polarization manipulation element is set to preserve orthogonal polarization components, the beam splitter separates the two-mode squeezed state into two distinct output modes — corresponding to the Fock-state regime. When the polarization components are aligned, the beam splitter causes them to interfere, producing two copies of single-mode squeezed vacuum states — suitable for Gaussian Boson Sampling. Intermediate settings of the polarization manipulation element allow the generation of mixed or hybrid squeezed states, enabling experimental investigation of transitional regimes. In other word, a single source architecture can generate both singlemode and two-mode squeezing, as well as hybrid squeezed states reducing hardware redundancy.

[0027] The light source as well as the optical quantum system comprising said light source is thus particularly suitable for use in photonic sampling experiments, such as Gaussian Boson Sampling and Fock State Boson Sampling, and enables efficient, and reconfigurable operation.

[0028] According to a preferred embodiment of the invention, the polarization manipulation element is a rotatable half-wave plate, and the light source is configured such that in a first rotational setting of the half-wave plate, the polarization components are directed to produce two-mode squeezed states, and in a second rotational setting of the half-wave plate, the polarization components interfere at the polarization-dependent beam splitter to produce two single-mode squeezed states. Preferably the rotational setting of the half-wave plate is with respect to the polarization axis of the incoming optical path. By exploiting polarization control switching between the distinct quantum state regimes is possible. In the first setting of the half-wave plate, the preferably orthogonally polarized output modes are preserved and directed into separate channels, maintaining their entanglement as a two-mode squeezed state, which is suited for Fock State Boson Sampling. In the second setting, the polarization components are rotated such that they become indistinguishable and interfere at the polarization beam splitter, thereby converting the output into two single-mode squeezed states for Gaussian Boson Sampling. The advantage of this configuration lies in its ability to support both experimental paradigms with a single source module, reducing hardware duplication and enabling reconfigurable operation without the need for optical realignment or replacement of components.

[0029] According to a preferred embodiment of the invention, the polarization manipulation element is adjustable in a continuously variable manner to enable real-time adjustment of the output squeezing regime. With regard to the half-wave plate, it is preferred that the half-wave plate is rotatable in a continuously variable manner. Continuous adjustment, as opposed to fixed- angle settings, permits dynamic modulation of the quantum state properties during operation. Rotatability of the half-wave plate can for example be implemented using motorized mounts or electronically controlled waveplate equivalents. Real-time adjustability allows for adaptive sampling protocols, feedback-controlled squeezing adjustment, or exploration of time-varying quantum phenomena within a single experimental run, thereby improving the flexibility and responsiveness of the quantum optical system.

[0030] In connection to this and according to a further preferred embodiment of the invention, the light source is configured such that in an intermediate setting between the first setting and the second setting of the polarization manipulation element, the light source produces quantum states that are a mixture of single-mode and two-mode squeezed states. This allows for finegrained control over the output state structure and enables experimental investigation of intermediate or hybrid squeezing regimes that lie between the established Gaussian and Fock- state sampling regimes. Such mixed-state operation opens new avenues for photonic sampling models and hybrid quantum-classical simulations.

[0031] Further preferably, the light source is tunable with respect to the degree of squeezing. The ability to continuously adjust the quantum state composition enhances the versatility of the system and facilitates systematic studies of quantum advantage thresholds and error-resilience under varying squeezing conditions.

[0032] According to a preferred embodiment of the invention, the light source is configured to emit polarization-entangled optical quantum states. By generating polarization-entangled outputs directly by the squeezed light source, the system eliminates the need for additional entanglement generation stages, simplifies the overall architecture, and improves the purity and coherence of the entangled states due to the waveguide’s stability and integration potential. According to another preferred embodiment of the invention, the light source further comprises as physical light source a laser in pulse mode. The pulsed laser as single physical light source enables the generation of well-defined temporal modes and high-peak-power pulses that are ideal for driving nonlinear processes such as parametric down-conversion in waveguides. The use of a pulsed source ensures high timing precision and compatibility with temporal multiplexing techniques. It also facilitates synchronization with external systems and detectors, which is essential for time-resolved quantum measurements. Preferably pulse shaping techniques are used to control the spectral and temporal profile of each quantum state, improving indistinguishability.

[0033] According to a further preferred embodiment of the invention, the waveguide-based twomode squeezer, the polarization control element, and the polarization-dependent beam splitter are implemented on an integrated photonic chip. Integration of all optical components onto a single chip significantly reduces optical losses, enhances thermal and mechanical stability, and enables compact, scalable fabrication. Integrated photonic chips allow for high-density component placement, making them suitable for large-scale quantum computing and sampling architectures. Furthermore, on-chip integration ensures precise phase control and alignment-free operation, which greatly reduces setup complexity and enhances reproducibility.

[0034] Further technical effects and advantages are directly derivable for the person skilled in the art from the below description of the optical quantum system comprising the light source.

[0035] As already mentioned, the invention is also directed to the optical quantum system for photonic sampling, wherein the system is configured to generate squeezed quantum states in the time domain and to interfere the quantum states in the spatial domain, the system comprising:

[0036] (a) the above-described light source, (b) the conversion element configured to map the temporally generated optical quantum states into spatially separated optical quantum states; and

[0037] (c) the spatially implemented linear optical network, configured to interfere the spatial separated optical quantum states.

[0038] In the optical quantum system, the light source is used as temporally multiplexed light source to generate the squeezed quantum states in the temporal domain. The light source enables the flexible preparation of either two-mode or single-mode squeezed states — or mixtures thereof — based on the setting of the polarization manipulation element, and preferably based on the rotational setting of the half-wave plate, and subsequent polarization control by the beam splitter. As a result, the system can support both Gaussian Boson Sampling and Fock State Boson Sampling protocols without requiring changes to the source hardware.

[0039] In addition to the light source, the system further comprises a conversion element configured to map the temporally generated optical quantum states into spatially separated optical quantum states. The temporally generated quantum states are then mapped into the spatial domain by means of the conversion element. This element separates successive time bins into individual spatial channels, allowing them to be processed in parallel. Once the quantum states have been converted into spatially separated channels, they are interfered within a spatially implemented linear optical network. The spatial configuration enables precise control over the optical transformation applied to the quantum states and supports full programmability of the linear optical network. The spatial implementation also allows for improved phase stability and compatibility with integrated photonic platforms.

[0040] According to a preferred embodiment of the invention, the optical quantum system is configured to implement Gaussian Boson Sampling, Fock State Boson Sampling, and a combination thereof. By enabling the dynamic tuning of the squeezing regime via the light source, the system can be adapted to different sampling protocols without requiring changes in the optical layout of the interferometer or the detection system. This architectural flexibility supports a wider range of experiments and allows for comparative studies across sampling regimes using a single experimental platform.

[0041] The conversion element may include, for example, a time-to-space demultiplexer and associated path-length compensation optics such as fiber loops. These components ensure that individual temporally generated squeezed states are distributed into separate spatial channels while maintaining their coherence and synchronization for high-visibility quantum interference.

[0042] The system also includes a spatially implemented linear optical network, such as an interferometer or a programmable integrated photonic chip, configured to interfere the spatially separated optical quantum states. The use of a spatial domain interferometer allows for precise control over the transformation applied to the quantum states and supports phasestable implementations that are particularly suitable for chip-based systems. By separating the generation of quantum states in the time domain from their interference in the spatial domain, the system architecture provides independent control over each process, enabling improved optimization, reduced losses, and enhanced scalability compared to monolithic time- or spacedomain architectures.

[0043] Additionally, the invention also relates to the method for performing photonic sampling experiments, preferably carried out using an optical quantum system configured as described above. The method comprises the steps of generating a sequence of squeezed optical quantum states in the time domain, and defining a degree of squeezing between two-mode squeezing and single-mode squeezing of the generated optical quantum states by adjusting a polarization manipulation element of a polarization control element. Preferably, the degree of squeezing is defined by rotating the rotatable half-wave plate of a polarization control element with respect to the polarisation axis of the generated sequence of squeezed optical quantum states. This adjustment allows the user to select the operational regime of the source in real time, thereby enabling not only Gaussian and Fock state Boson Sampling, but also the investigation of intermediate or hybrid sampling models.

[0044] The sequence of squeezed optical quantum states is generated in the time domain. Preferably, the generated states are then mapped into spatially separated channels by directing them into the spatial domain, preferably through a time-to-space conversion process. In a further preferred subsequent step, the spatially separated quantum states are interfered within a linear optical network to implement the sampling protocol. The combination of temporal generation, spatial interference, and polarization-based state tuning provides a versatile and experimentally efficient framework for exploring quantum photonic computational tasks.

[0045] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0046] The invention underlying this patent application was developed in a project funded by the BMBF under the project name “Phoquant”.

[0047] In the drawings:

[0048] Fig. 1 schematically shows a light source for an optical quantum system, according to a preferred embodiment of the invention.

[0049] Fig. 2 schematically shows an optical quantum system for photonic sampling, according to a preferred embodiment of the invention.

[0050] Fig. 1 schematically shows a light source 10 for an optical quantum system for photonic sampling, according to a preferred embodiment of the invention. The light source 10 comprises a waveguide-based two-mode squeezer 12, a polarization control element with a polarization manipulation element 14 and a polarization-dependent beam splitter 16. In this preferred embodiment the polarization manipulation element 14 of the polarization control element is a half-wave plate 14. The waveguide-based two-mode squeezer 12 is configured to generate squeezed optical quantum states from a single physical light source. The single physical light source is not shown in figure 1, however its output beam 18 is shown. The polarization control element with the half-wave plate 14 is arranged in an optical path of the generated optical quantum states of the two-mode squeezer 12. The polarization-dependent beam splitter 16 is arranged in an optical path of the output of the half-wave plate 14 and configured to separate or combine polarization components depending on a setting of the halfwave plate 14. The light source 10 is configured such that in a first rotational setting of the half-wave plate 14, the polarization components are directed to produce two-mode squeezed states, and in a second rotational setting of the half-wave plate 14, the polarization components interfere at the polarization-dependent beam splitter 16 to produce two singlemode squeezed states.

[0051] Fig. 2 schematically shows an optical quantum system 20 for photonic sampling, according to a preferred embodiment of the invention. The system 20 is configured to generate and manipulate optical quantum states 22 using a combination of temporal and spatial multiplexing techniques.

[0052] The system 20 comprises a temporally multiplexed squeezed light source 24 that produces a sequence of squeezed optical quantum states 22a in the time domain. In this preferred embodiment the temporally multiplexed squeezed light source 24 comprises a light source 10 as described above for figure 1 with a waveguide-based two-mode squeezer 12, a polarization control element with a polarization manipulation element 14 and a polarization-dependent beam splitter 16 in order to control the squeezing regime. Additionally, the temporally multiplexed squeezed light source 24 comprises as physical light source 26 a pulsed laser 26, operating at a high repetition rate and narrow pulse width to define the temporal modes. The output of the pulsed laser 26 is used for pulse shaping 28 in order to tailor the spectral and temporal properties of the pulses. Following pulse shaping 28, the squeezed optical states are generated by parametric down conversion with the waveguide-based two-mode squeezer 12. The resulting output consists of temporally ordered squeezed quantum states 22a suitable for multiplexing.

[0053] Furthermore, the system 20 comprises a conversion element 30 configured to map the temporally generated optical quantum states 22a into spatially separated optical quantum states 22b. The sequence of generated quantum states 12a is then transferred to the conversion element 30 that performs a domain transition from the time domain to the spatial domain. In this embodiment the conversion element 30 comprises a time-to-space converter 32 and a path compensation element 34. The time-to-space converter 32 includes a pulse demultiplexer 36 and an array of electro-optical modulators 38 that separate consecutive time bins into distinct spatial channels. Each temporal mode is switched into a different spatial output line, forming a set of spatially separated optical quantum states 22b. To ensure phase coherence and proper synchronization between these channels, the conversion element 30 further includes fibre loops 40 within the path compensation element 34. These loops 40 are adjusted such that each optical path length is equalized, compensating for differences arising from the differing arrival time of pulses. The fibre loops 40 are configured to isolate quantum states from different channels.

[0054] Furthermore, the system 20 comprises a spatially implemented linear optical network 42, configured to interfere the spatial separated optical quantum states 22b. The spatially separated quantum states 22b are directed into the spatially implemented linear optical network 42, which is in this embodiment configured as a programmable interferometer 42. The interferometer 42 is realized using an integrated photonic platform, enabling precise control of the optical transformation applied to the quantum states.

[0055] At the output of the interferometer 42, the quantum states are analysed by a photon detection element 44. In this embodiment the photon detection element 44 comprises a multi-channel array of superconducting nanowire single-photon detectors (SNSPDs), which are capable of photon-number-resolving detection with high timing resolution and efficiency. The output of the detectors is used to reconstruct the sampling distribution and to verify the performance of the quantum system 20 in executing a Boson Sampling protocol.

[0056] When using the system 20 the degree of squeezing between two-mode squeezing and singlemode squeezing of the generated optical quantum states 22a of the light source 10 can be adjusted by rotation of the half-wave plate 14.

[0057] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosed, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.

[0058] Reference signs list

[0059] 10 light source

[0060] 12 wave-guide based two mode squeezer

[0061] 14 polarization manipulation element

[0062] 16 polarization-dependent beam splitter

[0063] 18 output beam of physical light source

[0064] 20 optical quantum system

[0065] 22 optical quantum state

[0066] 22a sequence of squeezed optical quantum states

[0067] 22b spatially separated optical quantum states

[0068] 24 temporally multiplexed squeezed light source

[0069] 26 physical light source; laser

[0070] 28 pulse shaping

[0071] 30 conversion element

[0072] 32 time-to-space converter

[0073] 34 path compensation element

[0074] 36 pulse demultiplexer

[0075] 38 electro optical modulators

[0076] 40 fibre loops

[0077] 42 spatially implemented linear optical network; programmable interferometer

[0078] 44 photon detection element

Claims

C l a i m s1. Light source (10) for an optical quantum system (20) for photonic sampling, wherein the light source (10) comprises: a waveguide-based two-mode squeezer (12), configured to generate squeezed optical quantum states (12a) from a single physical light source (26); a polarization control element, comprising at least one polarization manipulation element (14) arranged in an optical path of the generated optical quantum states of the two-mode squeezer (12); and a polarization-dependent beam splitter (16), arranged in an optical path of an output of the polarization control element, and configured to separate or combine polarization components depending on a setting of the polarization manipulation element (14) of the polarization control element.

2. Light source (10) according to the previous claim, wherein the polarization manipulation element (14) is rotatable half-wave plate (14), and wherein the light source (10) is configured such that: in a first rotational setting of the half-wave plate (14), the polarization components are directed to produce two-mode squeezed states, and in a second rotational setting of the half-wave plate (14), the polarization components interfere at the polarization-dependent beam splitter to produce two single-mode squeezed states.

3. Light source (10) according to any of the previous claim, wherein the polarization manipulation element is adjustable in a continuously variable manner to enable realtime adjustment of the output squeezing regime.

4. Light source (10) according to any of the previous claims, wherein the light source (10) is configured such that in an intermediate setting between the first setting and the second setting of the polarization manipulation element (14), the light source (10) produces quantum states that are a mixture of single-mode and two-mode squeezed states.

5. Light source (10) according to any of the previous claims, wherein the light source (10) is configured to emit polarization-entangled optical quantum states.

6. Light source (10) according to any of the previous claims, further comprises as physical light source (26) a laser (26) in pulse mode.

7. Light source (10) according to any of the preceding claims, wherein the waveguidebased two-mode squeezer (12), the polarization control element, and the polarizationdependent beam splitter (16) are implemented on an integrated photonic chip.

8. An optical quantum system (20) for photonic sampling, wherein the system is configured to generate squeezed quantum states (22a) in the time domain and to interfere the quantum states in the spatial domain, the system (20) comprising:(a)a light source (10) being configured according to any of the previous claims,(b)a conversion element (30) configured to map the temporally generated optical quantum states (22a) into spatially separated optical quantum states (22b); and(c)a spatially implemented linear optical network (42), configured to interfere the spatial separated optical quantum states (22b).

9. System (20) according to the previous claim, wherein the system (20) is configured to implement Gaussian Boson Samling, Fock State Boson sampling and a combination thereof.

10. Method for performing photonic sampling experiments, preferably performed with an optical quantum system (20) configured according to any of the previous system claims, comprising the step: - generating a sequence of squeezed optical quantum states (22a) in the time domain, and- defining a degree of squeezing between two-mode squeezing and single-mode squeezing of the generated optical quantum states (22a) by adjusting a polarization manipulation element (14) of a polarization control element.

Images