Berlin 2012 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 89: Focus Session: Quantum Information Systems (jointly with MA,TT)

HL 89.5: Talk

Thursday, March 29, 2012, 17:45–18:00, ER 164

Noise spectroscopy using single-shot qubit readout — •Thomas Fink and Hendrik Bluhm — 2nd Institute of Physics C, RWTH Aachen University, 52074 Aachen, Germany

Understanding the noise limiting the dephasing time of qubits and mitigating its effects is crucial for improving qubit performance. For this purpose, dynamical decoupling schemes such as the spin echo and more sophisticated pulse sequences have been developed, which can also be used for noise spectroscopy. We propose an alternative method to investigate the magnitude of the bath fluctuations in the frequency domain using the correlations of single-shot measurements. It consists of correlating the single shot measurement outcomes of subsequent free induction decay pulses. Because our approach is applicable to a broad range of frequencies by simply varying the delay between pulses, it can give insight into spectral ranges where the sensitivity of pulse sequence-based spectroscopy is limited.

We compute the outcome of our procedure applied to GaAs-based electron spin-qubits, for which the coupling of the electron spins to ∼10⁶ nuclear spins of the host material has been identified as the dominant source of dephasing. We discuss how this procedure can be used to directly probe the suspected high frequency cutoff in the nuclear spin diffusion spectrum.

Comparing this procedure with spin-echo measurements may also reveal if the bath needs to be treated quantum-mechanically or can be considered as classical.