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Conference on Lasers and Electro-Optics

High-Speed Photodetection and Microwave Generation in a Sub-100 mK Environment

Josue Davila-Rodriguez, John D. Teufel, José Aumentado, Xiaojun Xie, Joe Charles Campbell, Scott A. Diddams, Franklyn Quinlan

Published May 5, 2019• 2 citations
Publisher

Abstract

We perform microwave generation via high-speed photodetection at a temperature of 20 mK. Shot noise-limited detection with high linearity was obtained, compatible with continued scaling of the control and readout of superconducting quantum information systems.© 2019 The Author(s)
DOI
10.23919/cleo.2019.8749255

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The photodetection of ultrashort optical pulse trains has applications in RF and microwave photonics systems that wish to take advantage of the exceptional frequency and timing precision available from optical sources. Room temperature applications include low phase noise microwave generation and sources for very long baseline interferometry, whereas cryogenic applications include driving quantum-based voltage standards and the drive and readout of superconducting qubits. Both room temperature and cryogenic applications of short pulse detection are reviewed.
Superconducting circuits have recently become a major contender for the implementation of quantum computers owing to their compatibility with existing microchip fabrication technologies. Their utility stems largely from their ability to be coupled with resonant cavities for the purposes of trapping and relaying microwave radiation. Because of this feature, scientists are able to transmit quantum information from a variety of qubits. Though quantum-limited amplifiers exist, unfortunately there currently exists no microwave photon counter capable of single shot quantum detection. Hence, we use superconducting circuits with Josephson junctions to design a microwave photon detector based on a modified phase qubit that exhibits a bandwidth of 4GHz, and a detection fidelity of 98%. We use metastable barrier transition (driven by incident photons) to create an avalanche effect analogous to current photo-diodes. Linear coupling of the junction flux with the radiation permits photodetection from an arbitrary quantum source in the GHz range. We show the device to be robust to changes in drive frequency, temporal photon width, and resonator quality factor, and we optimize our device with respect to these parameters. We show the device to be stable over the necessary time scales, and yet sensitive enough to accurately measure photons on demand.
The rapid development of superconducting quantum hardware is expected to run into substantial restrictions on scalability because error correction in a cryogenic environment has stringent input-output requirements. Classical data centres rely on fibre-optic interconnects to remove similar networking bottlenecks. In the same spirit, ultracold electro-optic links have been proposed and used to generate qubit control signals, or to replace cryogenic readout electronics. So far, these approaches have suffered from either low efficiency, low bandwidth or additional noise. Here we realize radio-over-fibre qubit readout at millikelvin temperatures. We use one device to simultaneously perform upconversion and downconversion between microwave and optical frequencies and so do not require any active or passive cryogenic microwave equipment. We demonstrate all-optical single-shot readout in a circulator-free readout scheme. Importantly, we do not observe any direct radiation impact on the qubit state, despite the absence of shielding elements. This compatibility between superconducting circuits and telecom-wavelength light is not only a prerequisite to establish modular quantum networks, but it is also relevant for multiplexed readout of superconducting photon detectors and classical superconducting logic.