Phase-Programmable Gaussian Boson Sampling Using Stimulated Squeezed Light

Abstract: The tantalizing promise of quantum computational speedup in solving certain problems has been strongly supported by recent experimental evidence from a high-fidelity 53-qubit superconducting processor1 and Gaussian boson sampling (GBS) with up to 76 detected photons. Analogous to the increasingly sophisticated Bell tests that continued to refute local hidden variable theories, quantum computational advantage tests are expected to provide increasingly compelling experimental evidence against the Extended Church-Turing thesis. In this direction, continued competition between upgraded quantum hardware and improved classical simulations is required. Here, we report a new GBS experiment that produces up to 113 detection events out of a 144-mode photonic circuit. We develop a new high-brightness and scalable quantum light source, exploring the idea of stimulated squeezed photons, which has simultaneously near-unity purity and efficiency. This GBS is programmable by tuning the phase of the input squeezed states. We demonstrate a new method to efficiently validate the samples by inferring from computationally friendly subsystems, which rules out hypotheses including distinguishable photons and thermal states. We show that our noisy GBS experiment passes the nonclassicality test using an inequality, and we reveal non-trivial genuine high-order correlation in the GBS samples, which are evidence of robustness against possible classical simulation schemes. The photonic quantum computer, Jiuzhang 2.0, yields a Hilbert space dimension up to $10^{43}$, and a sampling rate $10^{24}$ faster than using brute-force simulation on supercomputers.

• The paper presents a 144-mode phase-programmable Gaussian Boson Sampling experiment using high-brightness stimulated squeezed light, achieving up to 113 photon detection events.
• A novel stimulated squeezed light source improves photon purity and collection efficiency without narrowband filtering, enabling scalable GBS implementations.
• The study introduces robust validation strategies against classical spoofing and provides strong evidence of non-classicality, advancing the field towards practical quantum supremacy demonstrations.

A Comprehensive Overview of Phase-Programmable Gaussian Boson Sampling Using Stimulated Squeezed Light

The study presents an experiment leveraging Gaussian boson sampling (GBS) implemented within a 144-mode photonic circuit to achieve up to 113 photon detection events. This work advances the field of quantum computing by demonstrating a scalable high-brightness quantum light source based on the stimulated emission of squeezed light. The experiment introduces a programmable GBS model that allows for tunable phase inputs, providing a new and robust approach to validating quantum samples against classical simulation approaches.

Development of Stimulated Squeezed Light Sources

In exploring the potential of stimulated emission for increasing brightness in squeezed photon sources, a novel quantum light source was developed. By implementing a dual-pass configuration on PPKTP crystals to exploit stimulated parametric down-conversion, the researchers achieved significant enhancements in both purity and collection efficiency of the generated two-mode squeezed states (TMSS). The methodology resulted in photon sources with purity and efficiency values per crystal exceeding 0.96 and 0.91 respectively without the need for narrowband filtering, which signifies an improvement over prior techniques that faced trade-offs between brightness and other photonic attributes.

Experimental Setup and Interferometer Design

The experiment harnesses 25 high-purity TMSS sources channeled into a low-loss 144-mode interferometer, achieving a high overall system efficiency of 78%. Noteworthy is the device's sophisticated phase-locking system, which ensures phase coherence essential for GBS. The implementation of a continuous-wave laser system, combined with a multi-path phase-locking loop, enabled effective stabilization of phase fluctuation within a strict range to promote optimal input conditions and reduce interference-related adverse effects.

Validation Against Classical Hypotheses

The research introduces innovative strategies for corroborating the non-classicality of the GBS output, addressing possible spoofing scenarios involving distinguishable and thermal state photons, among others. This includes a method for inferring the validation of samples in computationally intractable regimes by examining subsystem modes. Bayesian tests revealed strong evidence excluding these mock hypotheses, even when analyzing larger mode subsystems. Simulated outcomes deviated significantly from the experimentally gathered distribution, reinforcing the fidelity of the quantum GBS data.

Implications and Prospects for Quantum Supremacy

This study's implications are profound, not only in further evidencing quantum computational advantage but also delineating practical enhancements needed for larger scale quantum photonic computing systems. By achieving data processing speeds many orders of magnitude faster than classical counterparts, with a Hilbert space dimension estimated at up to $10^{43}$, the study substantiates the field's advancement towards demonstrating feasible quantum supremacy.

The findings also open up new avenues for the application of the Jiuzhang 2.0 photonic quantum computer, particularly in areas such as quantum chemistry simulations, graph theory algorithms, and machine learning. The expandability of the TMSS sources tested within this study suggests scalability to broader quantum computing applications, bridging current theoretical capabilities with future real-world applications securely.

Conclusion

This work reflects a meaningful step forward in the field of quantum photonic technologies. The demonstrated use of stimulated squeezed light in a large-scale, programmable GBS represents both technical prowess and a strategic pathway towards increasingly complex quantum computing tasks. It is anticipated that continuous improvements in device efficiency, alongside robust validation techniques, will keep closing the gap between theoretical quantum advantage and empirical verification.