System and method for photonic sampling

Abstract

The invention relates to an optical quantum system (10) for photonic sampling, wherein the system (10) is configured to generate squeezed quantum states (12) in the time domain and to interfere the quantum states (12) in the spatial domain, the system comprising: (a) a temporally multiplexed squeezed light source (14), configured to generate a sequence of squeezed optical quantum states (12a) from a single physical light source (16); (b) a conversion element (18) configured to map the temporally generated optical quantum states (12a) into spatially separated optical quantum states (12b); and (c) a spatially implemented linear optical network (20), configured to interfere the spatial separated optical quantum states (12b). Furthermore, the invention relates to a method for performing photonic sampling experiments, preferably with the above optical quantum system (10).

Description

[0001] UNIVERSIT AT PADERBORN Dusseldorf, 16 September 2025

[0002] Our Reference: UD 42244 / SAM

[0003] Universitat Paderborn

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

[0005] System and method for photonic sampling

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

[0007] The present invention relates to an optical quantum system for photonic sampling, and in particular to a system capable of generating and interfering squeezed optical quantum states.

[0008] Furthermore, the present invention relates to a method for performing photonic sampling experiments, preferably performed with the above optical quantum system.

[0009] Photonic sampling experiments, such as Gaussian Boson Sampling or Fock State Boson Sampling play a central role in quantum information processing, particularly in the context of demonstrating quantum advantage and performing specific computational tasks that are believed to be classically intractable. In particular, Boson sampling has emerged as a tool to explore the advantages of quantum over classical computers as it does not require universal control over the quantum system, which favours current photonic experimental platforms. These experiments require the generation of squeezed optical quantum states, which must be precisely interfered and subsequently measured with detectors.

[0010] In the current state of the art, two principal architectures have been used to realize such systems. In the first, the generation and interference of quantum states are both implemented in the spatial domain. This typically involves a large number of identical physical sources, each producing a squeezed state that is directed through a spatially constructed beamsplitter network. Although this configuration is conceptually straightforward, it suffers from several disadvantages. The need for many discrete sources leads to high system complexity, increased costs, and a large physical footprint. Moreover, it is often difficult to ensure that the quantum states produced by different sources are indistinguishable. Reconfigurability is also limited, as each source is a fixed hardware component that cannot be easily adapted during operation.

[0011] In the second type of architecture, both generation and interference are carried out in the temporal domain. In this case, a single squeezed light source is used in pulsed mode to produce a train of time-separated quantum states. These states are delayed and synchronized using fiber loops and are then interfered in a time-based optical network. While this approach reduces the number of required physical sources, it introduces its own set of challenges. Light propagating through fiber loops is subject to optical losses and dispersion, which degrade the fidelity of the quantum states. Maintaining phase coherence between time-separated modes also demands advanced stabilization techniques. Furthermore, as the number of modes increases, the required number of components and delay lines grows significantly, limiting the scalability of the approach.

[0012] Therefore, there exists a need for an improved optical quantum system for Boson Sampling that allows for scalable, low-loss, and reconfigurable operation, while overcoming the architectural constraints of the prior art systems.

[0013] It is an objective to provide an optical quantum system for photonic sampling which overcomes at least one disadvantage of the prior art solutions. Preferably, it is an objective of the invention to provide an optical quantum system for photonic sampling that is scalable, has reduced hardware complexity and / or is reconfigurable.

[0014] The object is solved by the features of the independent claims. Preferred implementations are described in the sub claims. Thus, 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:

[0015] (a) a temporally multiplexed squeezed light source, configured to generate a sequence of squeezed optical quantum states from a single physical light source;

[0016] (b) a conversion element configured to map the temporally generated optical quantum states into spatially separated optical quantum states; and

[0017] (c) a spatially implemented linear optical network, configured to interfere the spatial separated optical quantum states.

[0018] Furthermore, the object is solved by a method for performing photonic sampling experiments, preferably performed with the above optical quantum system, comprising the steps:

[0019] - generating a sequence of squeezed optical quantum states in the time domain,

[0020] - generating spatially separated optical quantum states by mapping the generated optical quantum states into the space domain, and

[0021] - interfering the generated spatially separated optical quantum states in the space domain.

[0022] A common feature of architectures known in prior art is that both state generation and interference occur within the same domain, either spatial or temporal. The present invention however decouples the domains in which quantum states are generated and interfered, allowing each process to be implemented using the most suitable domain-specific techniques.

[0023] An aspect of the invention is thus, that the state generation is performed in the temporal domain, while the interference of the states is performed in the spatial domain - thereby enabling a more efficient and flexible design for photonic sampling experiments.

[0024] The system is particularly suitable for use in photonic sampling experiments, such as Gaussian Boson Sampling and Fock State Boson Sampling, and enables efficient, scalable, and reconfigurable operation. Squeezed quantum states are generated in the temporal domain using a temporally multiplexed light source. This allows multiple optical quantum states to be created from a single physical source, thereby reducing system complexity, enhancing spectral and temporal indistinguishability, and improving overall resource efficiency. The use of a single physical light source for state generation also enables compatibility with integrated waveguide-based sources, which offer high brightness and low loss.

[0025] 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.

[0026] 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.

[0027] By decoupling state generation and quantum interference into separate physical domains - temporal and spatial respectively - the invention enables independent optimization of each subsystem. This architectural separation improves the overall efficiency, flexibility, and scalability of the system and significantly reduces the limitations observed in prior art configurations.

[0028] According to a preferred embodiment of the invention, the temporally multiplexed squeezed light source comprises as physical light source a laser in pulse mode and uses pulse shaping and parametric down-conversion for the generation of the sequence of squeezed optical quantum states. This enables the generation of high-brightness, spectrally pure squeezed states with high temporal resolution. The use of a pulsed laser allows the generation of well- defined temporal modes, which are essential for multiplexing. Pulse shaping permits control over the spectral and temporal profile of each quantum state, improving indistinguishability. Parametric down-conversion, typically in a nonlinear medium such as a PPKTP waveguide, efficiently converts pump photons into pairs of correlated photons exhibiting squeezing. This combination ensures that the source delivers high-fidelity squeezed states in a compact and stable manner, suitable for integration.

[0029] According to a preferred embodiment of the invention, the conversion element comprises a time-to-space converter and a path compensation element. The time-to-space converter enables the mapping of the sequentially generated optical quantum states into parallel spatial channels, thereby allowing simultaneous interference in the spatial domain. To preserve coherence and synchronization across all spatial modes, the system preferably comprises the path compensation element that corrects for differential delays introduced during demultiplexing.

[0030] In connection to the above and according to a preferred embodiment of the invention, the time-to-space converter comprises a pulse demultiplexer and an array of electro-optical modulators. The pulse demultiplexer separates the sequence of squeezed pulses in time into individual spatial outputs, preferably through fast switching and / or dynamic routing. Electro- optical modulators (EOMs) provide high-speed control over the path of each pulse and allow dynamic reconfiguration of the routing behaviour. This architecture supports low-latency and low-loss temporal-to-spatial conversion. The fast switching provided by EOMs enables operation at high repetition rates, improving overall system throughput.

[0031] According to another preferred embodiment of the invention, the path compensation element comprises several individual fibre loops, configured such that no interference of the quantum states takes place in between different loops. The use of discrete fiber delay lines for each spatial output channel ensures accurate control of optical path lengths and avoids unintended mixing or interference between neighbouring quantum states. Each fiber loop introduces a well-defined delay corresponding to the time interval between consecutive pulses. By isolating the temporal modes within independent loops, coherence is preserved, thereby ensuring that interference only occurs at the intended stage — namely, within the spatially implemented optical network.

[0032] In connection to the spatially implemented linear optical network and according to a preferred embodiment of the invention, the spatially implemented linear optical network is implemented on an integrated platform. Integrated photonic platforms offer enhanced phase stability, compact form factors, and precise control over optical components such as beamsplitters and phase shifters. Implementing the linear optical network on such a platform allows for improved thermal and mechanical stability, reduced alignment requirements, and compatibility with high-density circuit layouts. This makes the system more scalable and reliable, while reducing the footprint and facilitating mass fabrication.

[0033] According to a preferred embodiment of the invention, the spatially implemented linear optical network is configured as a programmable interferometer. A programmable interferometer allows for dynamic control over the optical transformation applied to the input quantum states. By adjusting the internal phase settings or switching configurations, any arbitrary unitary operation can be implemented, including Haar-random unitaries commonly used in Boson Sampling experiments. Programmability enables the system to adapt to different sampling tasks and to be reused across multiple experiments without requiring physical reconfiguration, thereby enhancing versatility and reducing experimental turnaround time.

[0034] In this regard and according to a further preferred embodiment of the invention, the programmable interferometer is an integrated 12-mode optical chip. A 12-mode integrated interferometer provides sufficient dimensionality for demonstrating non-trivial Boson Sampling behaviour while remaining compact and experimentally manageable. Integration allows for precise control of the unitary transformation and facilitates synchronization with external components such as detectors and sources. The programmability of the chip ensures flexibility in implementing arbitrary linear optical networks, enabling advanced sampling experiments.

[0035] According to a further preferred embodiment of the invention, the system further comprises a photon detection element configured to detect the spatially interfered optical quantum states. Photon detection at the output of the spatially implemented linear optical network is used for registering the result of the sampling process. Accurate detection of spatially separated quantum states allows for the reconstruction of the output distribution and the statistical analysis of sampling data. The detection system must be sensitive to low light levels and capable of resolving individual photon events with minimal noise and timing jitter.

[0036] In connection to this and according to a further preferred embodiment of the invention, the photon detection element comprises a superconducting nanowire single-photon detector (SNSPD) array for photon number-resolved detection. SNSPDs offer high detection efficiency, preferably >90%, low timing jitter, preferably on the order of tens of picoseconds, and intrinsic photon-number-resolving capabilities. These features are critical for Boson Sampling applications, where the statistical distribution of multi-photon events across output modes encodes the computational outcome. The use of an SNSPD array ensures that high- quality, low-noise measurement data can be obtained with minimal loss, enabling faithful sampling from the quantum system’s output distribution.

[0037] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0038] The invention underlying this patent application was developed in a project funded by the BMBF under the project name “Phoquant”. In the drawings:

[0039] Fig. 1 schematically shows an optical quantum system for photonic sampling, according to a preferred embodiment of the invention.

[0040] Fig. 1 schematically shows an optical quantum system 10 for photonic sampling, according to a preferred embodiment of the invention. The system 10 is configured to generate and manipulate optical quantum states 12 using a combination of temporal and spatial multiplexing techniques.

[0041] The system 10 comprises a temporally multiplexed squeezed light source 14 that produces a sequence of squeezed optical quantum states 12a in the time domain. The light source includes a physical light source 16 implemented as a pulsed laser 16, operating at a high repetition rate and narrow pulse width to define the temporal modes. The output of the pulsed laser is used for pulse shaping 22 in order to tailor the spectral and temporal properties of the pulses.

[0042] Following pulse shaping 22, the squeezed optical states are generated by parametric down conversion 24 in a nonlinear medium, in this preferred embodiment a periodically poled waveguide. The resulting output consists of temporally ordered squeezed quantum states 12a suitable for multiplexing.

[0043] The sequence of generated quantum states 12a is then transferred to a conversion element 18 that performs a domain transition from the time domain to the spatial domain. This conversion element 18 comprises a time-to-space converter 26 and a path compensation element 28. The time-to-space converter includes a pulse demultiplexer 30 and an array of electro-optical modulators 32 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 12b. To ensure phase coherence and proper synchronization between these channels, the conversion element further includes fibre loops 34 within the path compensation element 28. These loops 34 are adjusted such that each optical path length is equalized, compensating for differences in the delay between channels. The fibre loops are configured to isolate quantum states from different channels.

[0044] The spatially separated quantum states 12b are then directed into a spatially implemented linear optical network 20, which is in this embodiment configured as a programmable interferometer 20. The interferometer 20 is realized using an integrated photonic platform, enabling precise control of the optical transformation applied to the quantum states.

[0045] At the output of the interferometer 20, the quantum states are analysed by a photon detection element 36. In this embodiment the photon detection element 36 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 10 in executing a Boson Sampling protocol.

[0046] This experimental configuration enables the efficient generation, demultiplexing, interference, and detection of quantum optical states using a hybrid temporal-spatial architecture. The architecture offers distinct advantages in terms of scalability, stability, integration capability, and compatibility with both Gaussian and Fock state Boson Sampling tasks.

[0047] 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.

[0048] Reference signs list

[0049] 10 system

[0050] 12 optical quantum state 12a sequence of squeezed optical quantum states

[0051] 12b spatially separated optical quantum states

[0052] 14 temporally multiplexed squeezed light source

[0053] 16 physical light source; laser

[0054] 18 conversion element 20 spatially implemented linear optical network; programmable interferometer

[0055] 22 pulse shaping

[0056] 24 parametric down-conversion

[0057] 26 time to space converter

[0058] 28 path compensation element 30 pulse demultiplexer

[0059] 32 electro optical modulators

[0060] 34 fibre loops

[0061] 36 photon detection element

Claims

C l a i m s1. An optical quantum system (10) for photonic sampling, wherein the system (10) is configured to generate squeezed quantum states (12) in the time domain and to interfere the quantum states (12) in the spatial domain, the system comprising:(a) a temporally multiplexed squeezed light source (14), configured to generate a sequence of squeezed optical quantum states (12a) from a single physical light source (16);(b) a conversion element (18) configured to map the temporally generated optical quantum states (12a) into spatially separated optical quantum states (12b); and(c) a spatially implemented linear optical network (20), configured to interfere the spatial separated optical quantum states (12b).

2. System (10) according to the previous claim, wherein the temporally multiplexed squeezed light source (14) comprises as physical light source (16) a laser (16) in pulse mode and uses pulse shaping (22) and parametric down-conversion (24) for the generation of the sequence of squeezed optical quantum states (12a).

3. System (10) according to any of the previous claims, wherein the conversion element (18) comprises a time to space converter (26) and a path compensation element (28).

4. System (10) according to claim 3, wherein the time to space converter (26) comprises a pulse demultiplexer (30) and an array of electro optical modulators (32).

5. System (10) according to claim 3 or 4, wherein the path compensation element (28) comprises several individual fibre loops (34), configured such that no interference of the quantum states (12) takes place in between different loops (34).

6. System (10) according to any of the previous claims, wherein the spatially implemented linear optical network (20) is implemented on an integrated platform, (advantage phase stability).

7. System (10) according to any of the previous claims, wherein the spatially implemented linear optical network (20) is configured as programmable interferometer (20).

8. System (10) according to any of the previous claims, wherein the programmable interferometer (20) is an integrated 12-mode optical chip.

9. System (10) according to any of the previous claims, wherein the system (10) further comprises a photon detection element (36) configured to detect the spatially interfered optical quantum states (12).

10. System according to claim 9, wherein the photon detection element (36) comprises a superconducting nanowire single-photon detector (SNSPD) array for photon number- resolved detection.

11. Method for performing photonic sampling experiments, preferably performed with an optical quantum system (10) configured according to any of the previous claims, comprising the steps:- generating a sequence of squeezed optical quantum states (12a) in the time domain,- generating spatially separated optical quantum states (12b) by mapping the generated optical quantum states (12a) into the space domain,- interfering the generated spatially separated optical quantum states (12a) in the space domain.

Images