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International Conference on Transparent Optical Networks

Squeezed light photon number statistics from a microresonator without photon number resolving detectors

Massimo Borghi, Emanuele Brusaschi, Marcello Bacchi, Marco Liscidini, Mattéo Galli, Daniele Bajoni

Published Jul 14, 2024• 0 citations
Publisher

Abstract

Measuring the photon number distribution (PND) of optical states allows one to extract metrics of non-classicality of fundamental and technological relevance, but requires in principle the use of detectors with photon number resolving capabilities (PNR). Here we reconstruct the PND of two-mode pulsed squeezed light generated from a silicon nitride microresonator using threshold detectors and variable optical attenuations. The PNDs are characterized up to $\sim 1.2$ photons/pulse, corresponding to an on-chip squeezing level of $6.2(2) \ \mathrm{dB}$ and a noise reduction factor (photon number difference squeezing) of $3.8(2) \ \mathrm{dB}$. The analysis performed on the photon-number basis allows us to additionally characterize the influence of a spurious thermal background field that reduces the photon number correlations.

DOI
10.1109/icton62926.2024.10647409

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Measuring the photon number distribution (PND) of optical states allows one to extract metrics of non-classicality of fundamental and technological relevance, but requires in principle the use of detectors with photon number resolving capabilities (PNR). Here we reconstruct the PND of two-mode pulsed squeezed light generated from a silicon nitride microresonator using threshold detectors and variable optical attenuations. The PNDs are characterized up to ∼1.2\sim 1.2∼1.2 photons/pulse, corresponding to an on-chip squeezing level of 6.2(2) dB6.2(2) \ \mathrm{dB}6.2(2) dB and a noise reduction factor (photon number difference squeezing) of 3.8(2) dB3.8(2) \ \mathrm{dB}3.8(2) dB. The analysis performed on the photon-number basis allows us to additionally characterize the influence of a spurious thermal background field that reduces the photon number correlations.
The measurement of the photon number distribution (PND) allows one to extract metrics of non-classicality of fundamental and technological relevance, but in principle it requires the use of detectors with photon number resolving (PNR) capabilities. In this work we reconstruct the PND of two-mode pulsed squeezed light generated from a silicon nitride microresonator using threshold detectors and variable optical attenuations. The PNDs are characterized up to ∼1.2 photons per pulse, through which we extracted an on-chip squeezing level of 6.2(2) dB and a noise reduction factor of −3.8(2) dB. The PNDs are successfully reconstructed up to a Hilbert space dimension of 6 × 6. The analysis performed on the photon number basis allows us to characterize the influence of a spurious thermal background field that spoils the photon number correlations. We evaluate the impact of self- and cross-phase modulation on the generation efficiency in case of a pulsed pump, and validate the results through numerical simulations of the master equation of the system.
Silicon nitride microresonators driven by strong pump pulses can generate squeezed light in a dominant spectral-temporal mode, a central resource for continuous-variable quantum computation. In the high parametric gain regime, several effects, including self- and cross-phase modulation as well as time-ordering corrections, become significant and can degrade source performance. In this work, we comprehensively investigate the generation of squeezed light from a silicon nitride resonator under pulsed pumping, spanning from low to high parametric gain up to approximately 16 photons/pulse. We experimentally study how the average photon number and the first- and second-order correlations of the squeezed marginal modes evolve with increasing pulse energy, across various frequency detunings and pulse durations. Furthermore, we analyze the errors introduced by multipair emissions in estimating the joint temporal intensity via time-resolved coincidence measurements. We propose and demonstrate an error-correction strategy based on the marginal distributions of time-resolved multiphoton events. Our results provide a practical strategy for optimizing the gain and the temporal mode structure of pulsed squeezed light sources in microresonators, elucidating the physical mechanisms and limitations that govern source performance in the high-gain regime.
A description of states of light in terms of photons allows for a clear delineation between classical and non-classical light. The development of single-photon sources and detectors has enabled experimental studies of quantum light at the single-photon level, proving essential for applications in quantum communication, sensing, and imaging. Multi-photon quantum states, existing in higher-dimensional spaces, extend these applications and open opportunities to study the rich space of non-classical light states. Platforms for sourcing and characterizing such states have been increasingly explored to leverage the quantum resources they offer. Arithmetic operations of photon addition and subtraction, allow for generating non-classical multi-photon light from classical sources like coherent and squeezed states, as well as for photon-number-resolved (PNR) detection. PNR detection is essential for characterizing multi-photon states,providing access to their photon-number distributions and higher-order correlations, and enabling advanced quantum tomography.
The work presented in this thesis aims to integrate sources and detectors of nonclassical states of light into a single photonic chip. Correlated pairs of single photons are among the most used sources in many quantum optics and quantum information experiments but their integration with detectors still remains a challenging task. In the first part of the thesis we exploit the generation of correlated pairs of photons in the visible spectrum using an integrated Silicon Nitride microring resonator. As the fabrication process of our sources is fully compatible with back-end CMOS technology, we also discuss the unique possibility of integration with silicon avalanche photodectors to provide a platform for commercially available, fully integrated, analogue quantum simulator working at room temperature. The drawback of universal quantum computation with single photons is its probabilistic nature that increases the technological complexity to obtain complete on chip integration of all necessary components to prepare, manipulate and measure quantum states of light. On the other hand, quantum information processing with continuous variables is completely deterministic. Therefore, in the second part of this work we report design, fabrication and experimental verification of an integrated source of broadband squeezed state of light on a photonic chip. We numerically investigate the amount of obtained squeezing and spurious noise that prevents us to observe shot noise reduction at short sideband frequencies. Additionally, we propose a design to extend our work towards hybridization with discrete variables to obtain qubits that can be protected against errors.
Squeezed light are optical beams with variance below the Shot Noise Level. They are a key resource for quantum technologies based on photons, they can be used to achieve better precision measurements, improve security in quantum key distribution channels and as a fundamental resource for quantum computation. To date, the majority of experiments based on squeezed light have been based on non-linear crystals and discrete optical components, as the integration of quadrature squeezed states of light in a nanofabrication-friendly material is a challenging technological task. Here we measure 0.45 dB of GHz-broad quadrature squeezing produced by a ring resonator integrated on a Silicon Nitride photonic chip that we fabricated with CMOS compatible steps. The result corrected for the off-chip losses is estimated to be 1 dB below the Shot Noise Level. We identify and verify that the current results are limited by excess noise produced in the chip, and propose ways to reduce it. Calculations suggest that an improvement in the optical properties of the chip achievable with existing technology can develop scalable quantum technologies based on light.