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arXiv:1504.04979 · Comptes Rendus Physique

Detecting itinerant single microwave photons

Sankar Raman Sathyamoorthy, Thomas M. Stace, Göran Johansson

Published Aug 1, 2016• 32 citations
arXivHTMLPDF

Abstract

Single-photon detectors are fundamental tools of investigation in quantum optics and play a central role in measurement theory and quantum informatics. Photodetectors based on different technologies exist at optical frequencies and much effort is currently being spent on pushing their efficiencies to meet the demands coming from the quantum computing and quantum communication proposals. In the microwave regime, however, a single-photon detector has remained elusive, although several theoretical proposals have been put forth. In this article, we review these recent proposals, especially focusing on non-destructive detectors of propagating microwave photons. These detection schemes using superconducting artificial atoms can reach detection efficiencies of 90% with the existing technologies and are ripe for experimental investigations.

DOI
10.1016/j.crhy.2016.07.010

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Single-photon detectors are fundamental tools of investigation in quantum optics and play a central role in measurement theory and quantum informatics. Photodetectors based on different technologies exist at optical frequencies and much effort is currently being spent on pushing their efficiencies to meet the demands coming from the quantum computing and quantum communication proposals. In the microwave regime, however, a single-photon detector has remained elusive, although several theoretical proposals have been put forth. In this article, we review these recent proposals, especially focusing on non-destructive detectors of propagating microwave photons. These detection schemes using superconducting artificial atoms can reach detection efficiencies of 90% with the existing technologies and are ripe for experimental investigations.
Single-photon detection is an essential component in many experiments in quantum optics, but it remains challenging in the microwave domain.We realize a quantum nondemolition detector for propagating microwave photons and characterize its performance using a single-photon source.To this aim, we implement a cavity-assisted conditional phase gate between the incoming photon and a superconducting artificial atom.By reading out the state of this atom in a single shot, we reach an external (internal) photon-detection fidelity of 50% (71%), limited by transmission efficiency between the source and the detector (75%) and the coherence properties of the qubit.By characterizing the coherence and average number of photons in the field reflected off the detector, we demonstrate its quantum nondemolition nature.We envisage applications in generating heralded remote entanglement between qubits and for realizing logic gates between propagating microwave photons.
Single-photon detection is an essential component in many experiments in quantum optics, but it remains challenging in the microwave domain. We realize a quantum nondemolition detector for propagating microwave photons and characterize its performance using a single-photon source. To this aim, we implement a cavity-assisted conditional phase gate between the incoming photon and a superconducting artificial atom. By reading out the state of this atom in a single shot, we reach an external (internal) photon-detection fidelity of 50% (71%), limited by transmission efficiency between the source and the detector (75%) and the coherence properties of the qubit. By characterizing the coherence and average number of photons in the field reflected off the detector, we demonstrate its quantum nondemolition nature. We envisage applications in generating heralded remote entanglement between qubits and for realizing logic gates between propagating microwave photons.
[EN] Single-photon photodetection of propagating microwaves is a long-standing question in the area of superconducting circuits. Initially, it was merely a scientific question, since applications of propagating quantum microwaves in the last decades did not requiere this device. However, it was recently proven its necessity for many novel applications related to quantum communications, distributed quantum computing with superconducting chips, and quantum radar. Here, we will study superconducting circuits and superconducting qubits in order to review a theoretical proposal for a working and efficient single-photon microwave photodetector.
Single-photon detectors are an essential part of the toolbox of modern quantum optics for implementing quantum technologies and enabling tests of fundamental physics. The low energy of microwave photons, the natural signal path for superconducting quantum devices, makes their detection much harder than for visible light. Despite impressive progress in recent years and the proposal and realization of a number of different detector architectures, the reliable detection of a single itinerant microwave photon remains an open topic. Here, we investigate and simulate a detailed protocol for single-photon multiplication and subsequent amplification and detection. At its heart lies a Josephson-photonics device which uses inelastic Cooper-pair tunneling driven by a dc bias in combination with the energy of an incoming photon to create multiple photons, thus compensating for the low-energy problem. Our analysis provides clear design guidelines for utilizing such devices, which have previously been operated in an amplifier mode with a continuous wave input, for counting photons. Combining a formalism recently developed by Mølmer to describe the full quantum state of in- and outgoing photon pulses with stochastic Schrödinger equations, we can describe the full multiplication and detection protocol and calculate performance parameters, such as detection probabilities and dark count rates. With optimized parameters, a high population of a single output mode can be achieved that can then be easily distinguished from vacuum noise in heterodyne measurements of quadratures with a conventional linear amplifier. Realistic devices with two multiplication stages with multiplication of 161616 reach for an impinging Gaussian pulse of length TTT a detection probability of 84.5%84.5\%84.5% with a dark count rate of 10−3/T10^{-3}/T10−3/T, and promise to outperform competing schemes.
Microwave quantum optics using superconducting circuits, also known as circuit QED, is a recent and promising field to study light-matter interactions at the fundamental level. In this field, artificial atoms made of superconducting elements interact with microwave photons routed through one dimensional transmission lines. This thesis is under the purview of circuit QED and is based on the three appended papers. In these three articles, we look at the problems of engineering photon-photon interaction (a la cross-Kerr effect) in microwaves using an artificial atom, storing and retrieving microwave photons using a tunable cavity and finally detecting a single propagating microwave photon non-destructively. The analysis is done using the framework of open quantum systems, where we use master equations and stochastic master equations to study the evolution of these artificial atoms in the presence of environment and under measurements respectively.
Superconducting quantum bits (qubits) are a leading candidate towards realizing a processor that is able to outperform existing classical computers at select tasks. One particular qubit architecture, the transmon, boasts long coherence times compared to required gate lengths and flexibility with respect to circuit couplings as these 'artificial atoms' are photolithographically defined. These attributes allow qubits to be leveraged for other tasks as well — such as efficiently detecting itinerant microwave photons. Such a device may prove useful for remote entanglement protocols, quantum optics experiments in the microwave regime, and as a detector for low-mass dark matter.Through a blend of circuit quantum electrodynamics (cQED) and waveguide quantum electrodynamics (wQED) theories, high detector performance was achieved even when the photon arrival time was not known. Utilizing an ensemble (N = 4) of identical transmon absorbers, photon mediated interactions along a common waveguide enable absorbed itinerant photons to be trapped for longer than the inverse of the bandwidth of an individual qubit. This extended trapping time allows for sufficient integration of the dispersively shifted readout resonator to resolve deviations from vacuum with high fidelity.