Ce séminaire aura lieu exceptionnellement un lundi.

Abstract : Spin 1/2 particles form native two level systems and thus lend themselves as a natural qubit implementation. However, encoding a single qubit in two (or more) spins entails the benefit of enabling fast, exchange driven control without the need for microwave pulses. Optimal performance of this approach typically requires large pulse amplitudes for fast control, which is prone to systematic errors and prohibits standard control approaches based on Rabi flopping. Furthermore, the exchange interaction typically used to electrically manipulate encoded spin qubits is inherently sensitive to charge noise. Depending on the host material system, dephasing due to nuclear spins can be an additional challenge. I will discuss all-electrical, high-fidelity single qubit operations for a spin qubit encoded in two electrons in a GaAs double quantum dot that address these difficulties. Starting from a set of numerically optimized control pulses [1], we employ an iterative tuning procedure based on measured error syndromes to remove systematic errors. Randomized benchmarking [2] yields an average gate fidelity of about 99 % and a leakage rate into invalid states below 0.1 %. I will briefly discuss first steps to adapt the approach to exchange-based two-qubit gates [3].

Time permitting, I will briefly present an example of how such control pulses can be adapted to the capabilities of dedicated qubit control circuits using pulse width instead of amplitude modulation, and conclude with a discussion of how cryoelectronics might enable the realization of large-scale quantum computing systems.

[1] Pascal Cerfontaine, Tim Botzem, David P. DiVincenzo, and Hendrik Bluhm, Phys. Rev. Lett. 113, 150501 (2014).

[2] P. Cerfontaine et al., Feedback-tuned noise-resilient gates for encoded spin qubits, arXiv:1606.01897 (2016).

[3] Sebastian Mehl, Hendrik Bluhm, and David P. DiVincenzo, Phys. Rev. B 90, 045404 (2014).

Contact : Hendrik Bluhm