Noise-resistant quantum memory enabled by Hamiltonian engineering

The mesoscopic nuclear spin ensemble in quantum dots, which consists of 10⁴ to 10⁶ nuclear spins and has a coherence time of up to milliseconds, is a promising candidate for a fast and scalable quantum memory. Coherently transferring the electron spin state to the collective nuclear spin state requires polarization of the nuclear spin ensemble. Nuclear spin noise can obstruct the transfer process and lower transfer fidelity especially at low nuclear polarization. Here we propose a new protocol for performing noise-resisted quantum state transfer by employing Hamiltonian engineering. By decoupling the nuclear spin noise from the electron with a sequence of pulses, while maintaining the necessary flip-flop interaction, our protocol guarantees high fidelity quantum state transfer at much lower nuclear polarizations. A numerical simulation that we conducted shows a fidelity over 80% can be reached as nuclear polarization drops to as low as 30%. This Hamiltonian engineering methods may also be helpful for future explorations in quantum memory and DNP in other systems such as NV color centers, doped-ion crystals and atomic ensembles.