Noise switching at a dynamical critical point in a cavity-conductor hybrid

Abstract

A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.ukNoise switching at a dynamical critical point in a cavity-conductor hybrid Coupling a mesoscopic conductor to a microwave cavity can lead to fascinating feedback effects which generate strong correlations between the dynamics of photons and charges. We explore the connection between cavity dynamics and charge transport in a model system consisting of a voltagebiased Josephson junction embedded in a high-Q cavity, focussing on the behavior as the system is tuned through a dynamical critical point. On one side of the critical point the noise is strongly suppressed, signalling the existence of a novel regime of highly coherent transport, but on the other side it switches abruptly to a much larger value. Using a semiclassical approach we show that this behavior arises because of the strongly nonlinear cavity drive generated by the Cooper pairs. We also uncover an equivalence between charge and photonic current noise in the system which opens up a route to detecting the critical behavior through straightforward microwave measurements.

Electronic and photonic counting statistics as probes of non-equilibrium quantum dynamics

“…In contrast to the photons leaking out of the cavity, the flow of Cooper pairs across the JJ is coherent, described by the current operator [21]…”

“…For systems consisting of a mesoscopic conductor coupled to a cavity mode, illustrated schematically in figure 1(a), charge flow generates a coherent photon flux entering the mode that is balanced by a leakage of radiation out into the wider electromagnetic environment and the mode itself can be thought of as a conductor, albeit a photonic one rather than an electrical one. From this perspective it is natural to ask how the counting statistics of the photons flowing in and out of the mode are related to the statistics of the charge current [20][21][22] and how they respond to the nonlinear quantum dynamics of the system. Indeed, measurements of photon statistics may reveal details of charge-charge correlations such as transitions between incoherent and coherent charge flow [21].…”

“…From this perspective it is natural to ask how the counting statistics of the photons flowing in and out of the mode are related to the statistics of the charge current [20][21][22] and how they respond to the nonlinear quantum dynamics of the system. Indeed, measurements of photon statistics may reveal details of charge-charge correlations such as transitions between incoherent and coherent charge flow [21].…”

“…In this article we address these issues focussing on a specific cavity-coupled conductor, a JJ biased at sub-gap voltages, where the connection between the flow of an electrical current and the generation of photons is particularly simple and the coupled quantum dynamics especially rich [2,8,9,21,[28][29][30][31][32][33][34][35]. A dc current flows at resonances where the energy available to tunnelling Cooper pairs matches that required to generate one or more cavity photons so that all of the energy from the voltage source is converted into photons [2,16], unlike in other conductors [17,20].…”

“…A dc current flows at resonances where the energy available to tunnelling Cooper pairs matches that required to generate one or more cavity photons so that all of the energy from the voltage source is converted into photons [2,16], unlike in other conductors [17,20]. Elsewhere we have explored how the current noise is linked to fluctuations in the flux of photons leaving the cavity [21]. Here we go much further, using a very general unitary transformation method to show that the FCS of photons and charges are related in a strikingly simple way.…”