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OSA Quantum 2.0 Conference

Real-Time Charge Control of Diamond Quantum Sensors

David A. Hopper, J. Lauigan, Tzu‐Yung Huang, Lee C. Bassett

Published Jan 1, 2020• 0 citations
Publisher

Abstract

We use real-time feedback to deterministically initialize a nitrogen-vacancy’s charge state at room temperature, and demonstrate improved spin readout efficiency resulting in a factor-of-20 speedup for a typical quantum sensing experiment.
DOI
10.1364/quantum.2020.qth5b.4

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Spin qubits based on nitrogen-vacancy centers in diamond are useful only when the defect exists in the correct charge state---but this state is usually uncontrolled, since it is sensitive to the optical fields used to interrogate the qubit. Using fast, real-time photon detection and control, the authors deterministically prepare the desired charge state and demonstrate that the qubit's performance as a magnetic sensor is dramatically improved. These experiments yield deeper understanding of the charge and spin dynamics of N-VVV centers, and the all-optical method can be adapted to dynamically control other stochastic properties of solid-state defects for improved performance.
A functioning qubit must be able to be initialized and measured. The fidelity of these operations is essential for all quantum applications, including quantum sensing, communication, and computation. The diamond nitrogen-vacancy (NV) center is a point defect in the lattice with an optical interface to a coherent ground-state spin, which makes the NV center one of the few spin qubits operable at room temperature. While the NV center spin state can be initialized and read out optically, the fidelity of these operations are far from perfect due to the charge and orbital dynamics. In typical conditions, the NV center is in the proper charge state 75% of the time, and measuring the spin state results in a non-zero signal only 1% of the time. These inefficient mechanisms make many measurements practically intractable. This thesis focuses on improving the preparation and measurement fidelities of NV centers through precise all-optical control of the charge, orbital, and spin dynamics. I first discuss an improved spin readout mechanism which relies on spin-to-charge conversion (SCC) and discuss the potential for single-shot spin readout. Following, I present how charge readout and SCC can be implemented in ensembles of NV centers within nanodiamonds and demonstrate that it provides improvements for spin-relaxometry studies. Finally, I develop a method for initializing a single NV center's charge state with real-time control and show that this capability improves spin readout performance for sensing. To conclude, I discuss how these improved initialization and readout capabilities can be applied to detecting and controlling coupled nuclear spins in the diamond lattice and consider other applications of real-time control.
Quantum sensors encompass a diverse class of devices that exploit quantum coherence to detect weak or nanoscale signals. As their behavior is tied to physical constants, quantum sensors can achieve accuracy, repeatability, and precision approaching fundamental limits [1, 2]. As a result, these sensors have shown utility in a wide range of applications in both science and engineering leading to innovations. Among many solid-state spin systems, nitrogen-vacancy (NV) centers in diamonds have attracted considerable attention as a leading platform in many fields of quantum technologies, from quantum sensing to information processing and communication applications. They have superior physical properties, and their quantum coherence is preserved even at room temperature. The energy levels of NV centers are sensitive to magnetic fields, electric fields, strain, and temperature, and the spatial resolution is scalable from nanometers to millimeters. Therefore, diamond quantum sensors are distinctive sensors with multimodality and span scalable application fields. To realize an ideal quantum sensor for applications, the technical challenges in the sensor materials and the quantum control techniques, such as coherent microwave spin manipulation, effective optical spin-state initialization, and readout, have been developed. This chapter briefly explains the sensing principle using NV centers and then introduces sensor systems for biomedical applications, and monitoring of batteries for electric vehicles and internal power devices.