סמינר בחומר מעובה: Increasing the coherence time of electronic spins in diamond - toward improved magnetic sensing and quantum information

Abstract:

Over the past several years a new research field has emerged, aimed at studying and utilizing specific defects in diamond, namely nitrogen vacancy (NV) color centers. The unique spin and optical properties of these defects position them as leading candidates for creating nanoscale quantum information building blocks (qubits) and magnetic nano-sensors.

One of the challenges that limits the performance of NV centers is decoherence, mostly due to an effective "spin bath noise" of random fluctuating magnetic fields caused by13C nuclear spins, Nitrogen (P1) electronic spins and other defects in the diamond. By overcoming the spin bath noise and increasing the coherence time of NV centers, higher magnetometric sensitivities can be achieved. Moreover, achievement of coherence times higher than typical NV-NV interaction time scales may pave the way toward the creation of interesting non-classical spin states.  For example, squeezed states are commonly created and used in optical systems, improving optical measurement sensitivities, but have not yet been created in the solid-state.

In this work we introduce theoretical and experimental approaches for analyzing and overcoming the spin bath noise. We suggest an original method for characterizing the noise properties using temporally misplaced Hahn-Echo microwave pulses. Using liquid nitrogen-based cooling and dynamical decoupling (DD) microwave controls, we experimentally demonstrate significant improvements in the coherence time of the spin state of a dense ensemble of NV centers. We characterize the effects of pulse and detuning errors, minimize our experimental imperfections, and compare the performance of various DD protocols. We identify that the optimal control scheme for preserving an arbitrary spin state is a symmetric and recursive protocol, the concatenated version of the XY8 pulse sequence. We achieve an order-of-magnitude improvement in the coherence of an arbitrary spin state, reaching a T2 coherence time of 30 ms.

מארגן הסמינר: פרופ' שמשון ברעד