Weak measurement of a solid-state qubit revealed in low-frequency noise

D. H. Slichter, Rajamani Vijay, Steve Weber +1 more

Lin Tian

Low-frequency noise presents a serious source of decoherence in solid-state qubits. When combined with a continuous weak measurement of the eigenstates, low-frequency noise induces a second-order relaxation between the qubit states. Here, we show that the relaxation provides a unique approach to calibrate the low-frequency noise in the time domain. By encoding one qubit with two physical qubits that are alternatively calibrated, quantum-logic gates with high fidelity can be performed.

Kristian Rabenstein, Viktor A. Sverdlov, D. V. Averin

Neil P. Oxtoby, Jay Gambetta, Howard M. Wiseman

The extension of quantum trajectory theory to incorporate realistic imperfections in the measurement of solid-state qubits is important for quantum computation, particularly for the purposes of state preparation and error correction as well as for readout of computations. Previously this has been achieved for low-frequency (dc) weak measurements. In this paper we extend realistic quantum trajectory theory to include radio frequency (rf) weak measurements where a low-transparency quantum point contact (QPC), coupled to a charge qubit, is used to damp a classical oscillator circuit. The resulting realistic quantum trajectory equation must be solved numerically. We present an analytical result for the limit of large dissipation within the oscillator (relative to the QPC), where the oscillator slaves to the qubit. The $\mathrm{rf}+\mathrm{dc}$ mode of operation is considered. Here the QPC is biased (dc) as well as subjected to a small-amplitude sinusoidal carrier signal (rf). The $\mathrm{rf}+\mathrm{dc}$ QPC is shown to be a low-efficiency charge-qubit detector, which may nevertheless be higher than the dc-QPC (which is subject to $1∕f$ noise).

Qiang Deng, D. V. Averin

Jason F. Ralph, Terrence D. Clark, M. J. Everitt +3 more