Cavity Photons as a Probe for Charge Relaxation Resistance and Photon Emission in a Quantum Dot Coupled to Normal and Superconducting Continua

Abstract

Microwave cavities have been widely used to investigate the behavior of closed few-level systems. Here, we show that they also represent a powerful probe for the dynamics of charge transfer between a discrete electronic level and fermionic continua. We have combined experiment and theory for a carbon nanotube quantum dot coupled to normal metal and superconducting contacts. In equilibrium conditions, where our device behaves as an effective quantum dot-normal metal junction, we approach a universal photon dissipation regime governed by a quantum charge relaxation effect. We observe how photon dissipation is modified when the dot admittance turns from capacitive to inductive. When the fermionic reservoirs are voltage biased, the dot can even cause photon emission due to inelastic tunneling to/from a BardeenCooper-Schrieffer peak in the density of states of the superconducting contact. We can model these numerous effects quantitatively in terms of the charge susceptibility of the quantum dot circuit. This validates an approach that could be used to study a wide class of mesoscopic QED devices.

Cavity QED with hybrid nanocircuits: from atomic-like physics to condensed matter phenomena

“…In equilibrium conditions, the charge relaxation dynamics caused by a fermionic reservoir can be studied with a high sensitivity. A first experiment seems consistent with a non-interacting theory which suggests the universality of the charge relaxation resistance in the adiabatic regime 37 . However, further study is required in the interacting case where a rich phenomenology is expected.…”

“…The transmission b t /b in of the cavity can be obtained experimentally by measuring the microwave amplitude b t going out through the output port, which can be the right port in Fig.1. In the semiclassical limit, the correspondence between the approach of section III B 1 and the inputoutput formalism of Circuit QED 86 gives the relations of Fig.5 between b in , b t(r) , ε in andā 37 .…”

“…This situation has been studied experimentally with carbon-nanotube quantum dots 37,54 . It is possible to control electrically the energy detuning ε d between the dot level and the Fermi energy of the reservoir (see Fig.…”

“…The rate of photon emission by the double dot can be estimated as Γ e n ω 0 /2Q 0 = 10 GHz, which is significantly larger than in Refs. 37,38 . Charge noise limits the maser linewidth.…”

Tunable photonic cavity coupled to a voltage-biased double quantum dot system: Diagrammatic nonequilibrium Green's function approach

“…Few examples of hybrid quantum systems include cavity-Quantum Electrodynamics (c-QED) arrays [2,[5][6][7], cold atoms coupled to light [8][9][10], optomechanical devices [11,12] and cavity-coupled quantum dots [2,[13][14][15][16][17][18][19][20][21]. The motivation for this paper is a class of recent experiments where quantum dots have been integrated with superconducting resonators, accomplishing sufficiently strong charge-cavity coupling of g ∼ 50 − 200 MHz [13,[22][23][24][25][26].…”