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Register a new userQuantum dynamics of a microwave resonator strongly coupled to a tunnel junction
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J\\'er\\^ome Est\\`eve
Publication date
2018
fields
Physics
and research's language is
English
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We consider the coupling of a single mode microwave resonator to a tunnel junction whose contacts are at thermal equilibrium. We derive the quantum master equation describing the evolution of the resonator field in the strong coupling regime, where the characteristic impedance of the resonator is larger than the quantum of resistance. We first study the case of a normal-insulator-normal junction and show that a dc driven single photon source can be obtained. We then consider the case of a superconductor-insulator-normal and superconductor-insulator-superconductor junction. There, we show that the Lamb shift induced by the junction gives rise to a nonlinear spectrum of the resonator even when the junction induced losses are negligible. We discuss the resulting dynamics and consider possible applications including quantum Zeno dynamics and the realization of a qubit.
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We study a single-mode cavity weakly coupled to a voltage-biased quantum point contact. In a perturbative analysis, the lowest order predicts a thermal state for the cavity photons, driven by the emission noise of the conductor. The cavity is thus emptied as all transmission probabilities of the quantum point contact approach one or zero. Two-photon processes are identified at higher coupling, and pair absorption dominates over pair emission for all bias voltages. As a result, the number of cavity photons, the cavity damping rate and the second order coherence $g^{(2)}$ are all reduced and exhibit less bunching than the thermal state. These results are obtained with a Keldysh path integral formulation and reproduced with rate equations. They can be seen as a backaction of the cavity measuring the electronic noise. Extending the standard $P(E)$ theory to a steady-state situation, we compute the modified noise properties of the conductor and find quantitative agreement with the perturbative calculation.
Quantum coherence in solid-state systems has been demonstrated in superconducting circuits and in semiconductor quantum dots. This has paved the way to investigate solid-state systems for quantum information processing with the potential benefit of scalability compared to other systems based on atoms, ions and photons. Coherent coupling of superconducting circuits to microwave photons, circuit quantum electrodynamics (QED), has opened up new research directions and enabled long distance coupling of qubits. Here we demonstrate how the electromagnetic field of a superconducting microwave resonator can be coupled to a semiconductor double quantum dot. The charge stability diagram of the double dot, typically measured by direct current (DC) transport techniques, is investigated via dispersive frequency shifts of the coupled resonator. This hybrid all-solid-state approach offers the potential to coherently couple multiple quantum dot and superconducting qubits together on one chip, and offers a method for high resolution spectroscopy of semiconductor quantum structures.
We consider a transmission line resonator which is driven by electrons tunneling through a voltage-biased tunnel junction. Using the Born-Markovian quantum master equation in the polaron basis we investigate the nonequilibrium photon state and emission spectrum of the resonator as well as properties of the transport current across the tunnel junction and its noise spectrum. The electroluminescence is optimized, with maximum peak height and narrow linewidth, when the back-action of the tunnel junction on the resonator and the decay rate of the resonator are similar in strength. For strong coupling between the resonator and tunnel junction, multi-photon effects show up in the noise spectrum of the transport current.
We propose a current correlation spectrum approach to probe the quantum behaviors of a nanome-chanical resonator (NAMR). The NAMR is coupled to a double quantum dot (DQD), which acts as a quantum transducer and is further coupled to a quantum-point contact (QPC). By measuring the current correlation spectrum of the QPC, shifts in the DQD energy levels, which depend on the phonon occupation in the NAMR, are determined. Quantum behaviors of the NAMR could, thus, be observed. In particular, the cooling of the NAMR into the quantum regime could be examined. In addition, the effects of the coupling strength between the DQD and the NAMR on these energy shifts are studied. We also investigate the impacts on the current correlation spectrum of the QPC due to the backaction from the charge detector on the DQD.
Achieving controllable coupling of dopants in silicon is crucial for operating donor-based qubit devices, but it is difficult because of the small size of donor-bound electron wavefunctions. Here we report the characterization of a quantum dot coupled to a localized electronic state, and we present evidence of controllable coupling between the quantum dot and the localized state. A set of measurements of transport through this device enable the determination of the most likely location of the localized state, consistent with an electronically active impurity in the quantum well near the edge of the quantum dot. The experiments we report are consistent with a gate-voltage controllable tunnel coupling, which is an important building block for hybrid donor and gate-defined quantum dot devices.
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