Persistent Rabi oscillations probed via low-frequency noise correlation

Abstract

The qubit Rabi oscillations are known to be non-decaying (though with a fluctuating phase) if the qubit is continuously monitored in the weak-coupling regime. In this paper we propose an experiment to demonstrate these persistent Rabi oscillations via low-frequency noise correlation. The idea is to measure a qubit by two detectors, biased stroboscopically at the Rabi frequency. The low-frequency noise depends on the relative phase between the two combs of biasing pulses, with a strong increase of telegraph noise in both detectors for the in-phase or anti-phase combs. This happens because of self-synchronization between the persistent Rabi oscillations and measurement pulses. Almost perfect correlation of the noise in the two detectors for the in-phase regime and almost perfect anticorrelation for the anti-phase regime indicates a presence of synchronized persistent Rabi oscillations. The experiment can be realized with semiconductor or superconductor qubits.The puzzle of the quantum state collapse due to measurement [1] is becoming accessible for the experimental study in solid state systems. Three experiments on non-projective collapse [2,3] have been recently realized with superconducting qubits. These experiments (as well as the experiment proposed in the present paper) touch upon the most intriguing property of quantum measurement: the presence of a "spooky" quantum back-action [4], which changes the system to agree with the observation, and cannot be explained in a realistic way, i.e. by using the Schrödinger equation.The quantum coherent (Rabi) oscillations in solid-state qubits are usually measured in an ensemble-averaged way [5,6] and decay within a short timescale, even though it can be much longer than the oscillation period. However, for a continuous weak measurement of a single qubit, the Rabi oscillations are non-decaying and can in principle be monitored in real time, as follows, e.g., from the quantum Bayesian formalism [7], which is generally similar to the formalism of quantum trajectories [8]. Persistence of the Rabi oscillations in this case is due to the quantum back-action, which tends to increase the amplitude of the oscillations to 100%, thus competing against decoherence. The persistent Rabi oscillations lead to the spectral peak of the detector signal at the Rabi frequency [9,10], which has been recently observed experimentally [3] (see also [11]). In the present paper we will discuss another way of demonstrating these oscillations.For definiteness let us discuss a "charge" qubit made of a double quantum dot (DQD) populated by a single electron, the location of which is continuously measured by a nearby quantum point contact (QPC). Analogous setups can be realized with spin-based or superconducting qubits. The continuous qubit evolution due to the quantum "informational" back-action can in principle be verified in a direct experiment [7]; however, it would require high-bandwidth recording of the detector signal (including shot noise) and fast qubit manipulation, that is still a big chall...

Rabi-vibronic resonance with large number of vibrational quanta

“…Instead, the oscillator motion gets synchronized with the Rabi oscillations. In this regard, there is certain analogy to the synchronization of the Rabi oscillations to a sequence of pulses 21 applied to the detector with repetition period chosen to be 2π/Ω R .…”

Continuous measurements for control of superconducting quantum circuits

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Measurement Back-Action in Quantum Point-Contact Charge Sensing

“…Interesting prospects of correlation measurements have been proposed e.g., in Refs. [35] and [36]. Unfortunately, the correlation analysis cannot be directly applied to the spin-qubit readout method used, e.g., in [3]; the reason is that in this case, the measured tunneling process is not fully random (Poissonian) but is regularized using a periodic gate pulse scheme.…”