Heisenberg-limited spin squeezing in a hybrid system with silicon-vacancy centers.

In this paper, we investigate the spin squeezing in a hybrid quantum system consisting of a Silicon-Vacancy (SiV) center ensemble coupled to a diamond acoustic waveguide via the strain interaction. Two sets of non-overlapping driving fields, each contains two time-dependent microwave fields, are applied to this hybrid system. By modulating these fields, the one-axis twist (OAT) interaction and two-axis two-spin (TATS) interaction can be independently realized. In the latter case the squeezing parameter scales to spin number as ξ R2∼1.61N -0.64 with the consideration of dissipation, which is very close to the Heisenberg limit. Furthermore, this hybrid system allows for the study of spin squeezing generated by the simultaneous presence of OAT and TATS interactions, which reveals sensitivity to the parity of the number of spins Ntot, whether it is even or odd. Our scheme enriches the approach for generating Heisenberg-limited spin squeezing in spin-phonon hybrid systems and offers the possibility for future applications in quantum information processing.

Deterministic generation of entanglement states between Silicon-Vacancy centers via acoustic modes.

We propose a scheme to entangle Silicon-Vacancy (SiV) centers embedded in a diamond acoustic waveguide. These SiV centers interact with acoustic modes of the waveguide via strain-induced coupling. Through Morris-Shore transformation, the Hilbert space of this hybrid quantum system can be factorized into a closed subspace in which we can deterministically realize the symmetrical Dicke states between distant SiV centers with high fidelity. In addition, the generation of entangled Dicke states can be controlled by manipulating the strength and frequency of the driving field applied on SiV centers. This protocol provides a promising way to prepare multipartite entanglement in spin-phonon hybrid systems and could have broad applications for future quantum technologies.

Cascaded on-chip phonon shield for membrane microresonators.

We propose to suppress acoustic wave coupling between a Si3N4 membrane resonator and its support structure through cascaded low-frequency resonators fabricated on the silicon substrate of the membrane. The on-chip silicon resonators are designed to ensure that the frequencies of their oscillatory motion are well separated from the mechanical modes of the membrane resonator. Using optical interferometry, we characterize the displacement response of the membrane frame with the vibration isolation; mechanical isolation >30 dB from the mounting surface is achieved. Thus, we reliably fabricate Si3N4 membrane resonators with mechanical quality factors of around 2×106 at room temperature.