Autonomous calibration of single spin qubit operations

Abstract

Fully autonomous precise control of qubits is crucial for quantum information processing, quantum communication, and quantum sensing applications. It requires minimal human intervention on the ability to model, to predict, and to anticipate the quantum dynamics, as well as to precisely control and calibrate single qubit operations. Here, we demonstrate single qubit autonomous calibrations via closed-loop optimisations of electron spin quantum operations in diamond. The operations are examined by quantum state and process tomographic measurements at room temperature, and their performances against systematic errors are iteratively rectified by an optimal pulse engineering algorithm. We achieve an autonomous calibrated fidelity up to 1.00 on a time scale of minutes for a spin population inversion and up to 0.98 on a time scale of hours for a single qubit π 2 -rotation within the experimental error of 2%. These results manifest a full potential for versatile quantum technologies.npj Quantum Information (2017) 3:48 ; doi:10.1038/s41534-017-0049-8 INTRODUCTIONThe ability to precisely control and calibrate single qubit operations in solids is a key element for reliable and scalable high-performance quantum technologies, for instance quantumenhanced sensors and metrological devices. It is also the backbone of many quantum information processing tasks, which paves the way for the future realisation of quantum computation and communication. Together with efficient quantum system characterisations and dynamical predictions, 1,2 where human intervention is minimised, autonomous calibration of a single spin qubit is necessary for the realisation of such advanced quantum technologies. We report here experimental demonstrations of the autonomous calibration of a single spin qubit in diamond using closed-loop optimisation. Our spin qubit implementation is a single nitrogen-vacancy (NV) colour centre in diamond. It provides a suitable platform for a precise qubit manipulation to be realised. 3,4 Its remarkable features, such as optical initialisation and readout, and the ability to be manipulated by microwave fields at room temperature, make this physical system extremely attractive for many quantum technologies. 5 We have witnessed a vast array of demonstrations of the NV centres showing a great potential for future technologies, ranging from sub pico-Tesla magnetometry, 6 electric field and temperature sensing, 7,8 to probing molecular dynamics, 9 and single-cell magnetic imaging. 10 Furthermore, intertwinements between quantum information and metrology using NV centre-based systems yield novel and effective techniques towards the realisation of high-performance technologies, e.g. applying quantum error correction 11 and phase estimation 12 to improve magnetic field sensitivity. One way to reach such technology is to apply the closed-loop optimisation method for auto-calibrating the controls required to drive the system in the presence of experimental limitations and noise. Closed-loop optimal control has been already applied...

Amplification of the parametric dynamical Casimir effect via optimal control

“…Moreover, if closed loop optimal control is employed, the optimization incorporates unknown and unpredictable drifts into the pulse design as well as makes the pulses robust against statistical disturbances (noise on the pulses and the figure of merit) [33,41,43]. Indeed, we could confirm the robustness of the optimal strategies by numerical simulations of the system evolution steered by the optimized dCRAB pulse (from Fig.…”

“…Finally, we point out that the optimal pulses identified here are expected to work equally well in a (reasonable) noisy environment, due to their intrinsic robustness against small variations, as it has been already theoretically and experimentally showed in many different scenarios [28,[40][41][42][43][44]. Moreover, if closed loop optimal control is employed, the optimization incorporates unknown and unpredictable drifts into the pulse design as well as makes the pulses robust against statistical disturbances (noise on the pulses and the figure of merit) [33,41,43].…”

Self-Consistent Calibration of Quantum-Gate Sets

“…Once gate errors have been characterized, they can be corrected by manual or automatic tuning of the available parameters. Automatic tuning is indispensable for scaling up to many qubits and to systematically deal with non-orthogonal gate parameters and cross-talk [8][9][10][11][12][13][14] . The moderate resource requirements of GSC are especially advantageous for automated calibration, which feeds the extracted gate errors into an iterative optimization algorithm (from now on referred to as solver).…”

Robust and efficient quantum optimal control of spin probes in a complex (biological) environment. Towards sensing of fast temperature fluctuations

“…To counteract variations in the NV spin transitions frequency and its driving strength, one can utilize optimal control theory, which has been used for NV spin control in a variety of applications [18][19][20][21][22]. In general, the strategy is to numerically optimize a pulse to achieve a desired quantum state.…”