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New Journal of Physics

Enhancement of single-photon level signal detection based on phase sensitive amplification strategy

Changchang Zhang, Zhaolu Wang, Hongjun Liu, Nan Huang

Published Oct 1, 2024• 2 citations
Publisher

Abstract

Abstract We investigate the ability of phase-sensitive amplification (PSA) to noiselessly amplify the preferred quadrature components of single-photon signals that are limited by phase fluctuations relative to the pump. We present a PSA enhancement strategy that is more realistic for possible experimental realization and is expected to significantly improve the detection of weak signals at the single-photon level and obtain more useful information. Our study shows that with a large PSA gain, proper transmissivity allows both direct and balanced homodyne detections to operate optimally simultaneously, and effectively improves the noise figure degradation owing to the internal losses and non-ideal detection efficiency.

DOI
10.1088/1367-2630/ad8778

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Abstract We investigate the ability of phase-sensitive amplification (PSA) to noiselessly amplify the preferred quadrature components of single-photon signals that are limited by phase fluctuations relative to the pump. We present a PSA enhancement strategy that is more realistic for possible experimental realization and is expected to significantly improve the detection of weak signals at the single-photon level and obtain more useful information. Our study shows that with a large PSA gain, proper transmissivity allows both direct and balanced homodyne detections to operate optimally simultaneously, and effectively improves the noise figure degradation owing to the internal losses and non-ideal detection efficiency.
We demonstrate a balanced-homodyne LADAR receiver employing a phase-sensitive amplifier (PSA) to raise the effective photon detection efficiency (PDE) to nearly 100%. Since typical LADAR receivers suffer from losses in the receive optical train that routinely limit overall PDE to less than 50% thus degrading SNR, PSA can provide significant improvement through amplification with noise figure near 0 dB. Receiver inefficiencies arise from sub-unity quantum efficiency, array fill factors, signal-local oscillator mixing efficiency (in coherent receivers), etc. The quantum-enhanced LADAR receiver described herein is employed in target discrimination scenarios as well as in imaging applications. We present results showing the improvement in detection performance achieved with a PSA, and discuss the performance advantage when compared to the use of a phase-insensitive amplifier, which cannot amplify noiselessly.
Phase-sensitive amplification (PSA) can enhance the signal-to-noise ratio (SNR) of an optical measurement suffering from detection inefficiency. Previously, we showed that this increased SNR improves LADAR-imaging spatial resolution when infinite spatial-bandwidth PSA is employed. Here, we evaluate the resolution enhancement for realistic, finite spatial-bandwidth amplification. PSA spatial bandwidth is characterized by numerically calculating the input and output spatial modes and their associated phase-sensitive gains under focused-beam pumping. We then compare the spatial resolution of a baseline homodyne-detection LADAR system with homodyne LADAR systems that have been augmented by pre-detection PSA with infinite or finite spatial bandwidth. The spatial resolution of each system is quantified by its ability to distinguish between the presence of 1 point target versus 2 closely-spaced point targets when minimum error-probability decisions are made from quantum limited measurements. At low (5-10 dB) SNR, we find that a PSA system with a 2.5kWatts pump focused to 25μm × 400μm achieves the same spatial resolution as a baseline system having 5.5 dB higher SNR. This SNR gain is very close to the 6 dB SNR improvement possible with ideal (infinite bandwidth, infinite gain) PSA at our simulated system detection efficiency (0.25). At higher SNRs, we have identified a novel regime in which finite spatial-bandwidth PSA outperforms its infinite spatial-bandwidth counterpart. We show that this performance crossover is due to the focused pump system's input-to-output spatial-mode transformation converting the LADAR measurement statistics from homodyne to heterodyne performance.
Quantum noise fundamentally limits the performance of fiber-optic systems beyond the standard quantum limit (SQL), restricting long-distance quantum key distribution, quantum communication, and precision quantum sensing. To overcome these limitations, quantum-squeezed states enable quadrature-dependent noise suppression, yet their benefits rapidly degrade under fiber attenuation, necessitating low-noise amplification. Since conventional phase-insensitive amplifiers (PIAs) impose a minimum 3 dB noise figure (NF) penalty and disrupt quantum correlations, phase-sensitive amplification (PSA) becomes essential. In this work, we propose a PSA based on dual-pump frequency-degenerate four-wave mixing (FWM) to amplify weak coherent squeezed states. Here, the PSA is seeded by an information-carrying single-mode squeezed state, where the information is encoded in the displacement degree of freedom, rather than in the squeezing itself. By optimizing the relative phases among the squeezed state, pump fields, and weak signal, the scheme maintains proper squeezing alignment and preserves the encoded quantum correlations during propagation. Under low-loss conditions, it is shown that the effective NF reaches −7.787 dB, demonstrating that the scheme enables quantum-limited amplification suitable for long-haul transmission and offering a viable path toward scalable fiber-based quantum technologies.
Quantum states are essential resource for quantum-enhanced applications. Loss incurred in the distribution channel, however, dissipates the high signal-to-noise ratio advantage enjoyed by the squeezed state. Here, we first demonstrate noise immunity enhancement by using phase-sensitive amplifier (PSA) with measurement-based noiseless linear amplifier (MB-NLA). We explore the signal transfer capability with the amplifier in a noisy channel. The MB-NLA enhanced PSA has obvious suppression effect on channel noises, especially it has improvement for the noise contaminated signal. Better performance can be achieved by flexibly adjusting amplifier parameters. With the amplifier, it is promising to overcome the entanglement-distribution loss and show its superiority in squeezing based quantum sensing.
Phase-sensitive amplification (PSA) can significantly improve the degradation caused by inefficient detectors in squeezing-based precision measurements. However, broadband incident light will lead to non-perfect PSA. The present work focused on the enhancement of non-perfect PSA for squeezed states with broad bandwidth for the measurement of weak absorption detection. Numerical calculations of the quantum advantage show that non-perfect PSA can effectively improve the inefficiency of detection in slight drift frequency detuning.
In optical communication systems, Phase Sensitive Amplifier (PSA) is well known for its superior noise performance in the sub-quantum limit. Therefore, PSAs are highly suitable for long haul transmission systems where amplification and regeneration is critical. In this paper, we analyze the gain performance of a single pump non-degenerate PSA operating in the quadratic gain regime. The variation of gain characteristics with pump power and fiber length has been discussed. It could be seen that for a 5km long fiber, increasing of pump power above 4W subjected to the increasing of amplifier gain while maintaining the relative phase at a stable constant value of 0.001 rad. Therefore, by fine tuning parameters like fiber nonlinearity, pump power and fiber length, a phase stabilized gain performance of the PSA could be achieved when it is operating in the quadratic gain regime.