Many body physics with NV centers in diamond
Entering the realm of many-body physics, we investigate the quantum dynamics of an interacting spin ensemble embedded in diamond. Our spins of choice are nitrogen-vacancy (NV) centers which allow us to perform quantum simulations even at room temperature, thanks to their remarkable properties such as long coherence time, high fidelity optical readout and state initialization, as well as coherent control with microwaves. In addition, NV centers can interact via long-range dipole-dipole interactions, creating quantum entanglement. Disorder is also a key parameter that significantly influences the dynamics of the spin system, and occurs naturally due to the presence of other paramagnetic impurities and lattice strain in diamond.
Our black diamond sample hosts a high concentration of NV centers, offering the intriguing possibility to probe the intricate, long-time dynamics of a long-range interacting spin ensemble which cannot be easily simulated by a classical computer. For the past few years, we have investigated various quantum phenomena resulting from the interplay between interaction and disorder. A few highlights are:
Slow thermalization in a disordered, dipolar spin system
We have studied how a large quantum system consisting of millions of spins can thermalize over time due to their intrinsic many-body dynamics. We demonstrate that in a three-dimensional system, complete loss of quantum information occurs on a critically slow timescale due to the interplay of spin-exchange interactions and disorder. The slow thermalization dynamics, which follow a power-law decay, can be tuned by the strength of disorder.
Depolarization dynamics of a strongly interacting spin ensemble
We observed that longitudinal spin relaxation (T1) is anomalously enhanced in the high-density sample, shortening T1 to only a few tens of microseconds. We found that optical excitation used for spin state initialization can induce, as a side effect, significant charge instability of the defects inside the diamond. This in turn gives rise to incoherent spin diffusion to the environment, rapidly depolarizing the NV centers. Suppressing such unwanted coupling to the environment is of our current interest.
Observation of discrete time-crystalline order
Recently, it has been theoretically proposed that periodically driven systems can display an exotic phase of matter dubbed a discrete time crystal, breaking the discrete time-translational symmetry of the drive. Using strongly interacting dipolar spins subject to periodic driving, we experimentally observed such discrete time-crystalline order featuring strong robustness against perturbations. Currently, we are investigating its potential as a probe of thermalization dynamics as well as potential applications in quantum metrology.
References:
G. Kucsko et. al. Phys. Rev. Lett. 121, 023601 (2018).
J. Choi et. al. Phys. Rev. Lett. 118, 093601 (2017).
S. Choi et. al. Nature 543: 221-225 (2017).