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Optica

Cryogenic feedforward of a photonic quantum state

Frederik Thiele, Niklas Lamberty, Thomas Hummel, Nina Amelie Lange, Lorenzo M. Procopio, Aishi Barua, Sebastian Lengeling, Viktor Quiring, Christof Eigner, Christine Silberhorn, Tim J. Bartley

Published Apr 14, 2025• 7 citations
Publisher

Abstract

Modulation conditioned on measurements on entangled photonic quantum states is a cornerstone technology of optical quantum information processing. Performing this task with low latency requires combining single-photon-level detectors with both electronic logic processing and optical modulation in close proximity. Here, we demonstrate low-latency feedforward using a quasi-photon-number-resolved measurement on a quantum light source. Specifically, we use a multipixel superconducting nanowire single-photon detector, amplifier, logic, and an integrated electro-optic modulator in situ below 4 K. We modulate the signal mode of a spontaneous parametric down-conversion source, conditional on a photon-number measurement of the idler mode, with a total latency of (23±3)ns. Furthermore, we investigate the resulting change in the photon statistics. This represents an important benchmark for the fastest quantum photonic feedforward experiments comprising measurement, amplification, logic, and modulation. This has direct applications in quantum computing, communication, and simulation protocols.

DOI
10.1364/optica.551287

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Modulation conditioned on measurements on entangled photonic quantum states is a cornerstone technology of optical quantum information processing. Performing this task with low latency requires combining single-photon-level detectors with both electronic logic processing and optical modulation in close proximity. In the technologically relevant telecom wavelength band, detection of photonic quantum states is best performed with high-efficiency, low-noise, and high-speed detectors based on the photon-induced breakdown of superconductivity. Therefore, using these devices for feedforward requires mutual compatibility of all components under cryogenic conditions. Here, we demonstrate low-latency feedforward using a quasi-photon-number-resolved measurement on a quantum light source. Specifically, we use a multipixel superconducting nanowire single-photon detector, amplifier, logic, and an integrated electro-optic modulator in situ below 4K. We modulate the signal mode of a spontaneous parametric down-conversion source, conditional on a photon-number measurement of the idler mode, with a total latency of (23+/-3)ns. The photon-number discrimination actively manipulates the signal mode photon statistics, which is itself a central component in photonic quantum computing reliant on heralded single-photon sources. This represents an important benchmark for the fastest quantum photonic feedforward experiments comprising measurement, amplification, logic and modulation. This has direct applications in quantum computing, communication, and simulation protocols.
Interfacing single-photon detectors with active photonic components is a cornerstone photonic quantum technology. We describe how the output signal of commercial superconducting nanowire single-photon detectors can be used in situ to drive photonic components such as lasers and electro-optic modulators, co-located in the cryostat. This is enabled by developing custom circuitry using cryogenic-compatible discrete components in the SiGe-BiCMOS platform. We have demonstrated this with a number of experiments, in particular optical readout of an SNSPD and low-latency feed-forward modulation based on single-photon measurement events, all at or below 4 K. This manuscript is an abridged version of the Master thesis of the primary author N. Lamberty.
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The realisation of light modulation based on single photon detection events is an important step towards feed-forward-modulation, which is required for many quantum optics protocols. This requires combining detection events with modulation in a device with a small physical footprint, for which integrated optics is ideal. Several platforms for integrated quantum optics have been developed to generate, modulate, and detect quantum features in the light over the last years. Titanium in-diffused waveguides in lithium niobate is a promising candidate for quantum communication applications [1] , [2] , however, single photon detection with superconducting photon detectors (SNSPDs) require cryogenic temperatures. Therefore, optimising the nonlinear optical properties of these waveguides under cryogenic operating conditions is an important task. Previously, we have demonstrated frequency conversion [3] , electro-optical modulation [4] and integrated single photon detection [5] at cryogenic temperatures.