Interfacing spins and mechanical degrees of freedom allows for a variety of applications and interesting experimental observations. On one hand, one can use the dynamics of the mechanical resonator to mediate coupling between individual spins [1]. Such an approach can be scaled up to enable mechanically mediated interactions between many qubits on a single chip [2], or even programmable interactions between individual qubits [2]. On the other hand, being a nonlinearity quantum system, the spin can also be used to manipulate the mechanical state and even prepare the latter in exotic quantum states. Additionally, the mechanical resonator can also be cooled to its ground state with either the spin or established optomechanical techniques.

In our lab, we aim to achieve coherent coupling of nitrogen vacancy (NV) center spin qubits in diamond, to mechanical resonators via a magnetic field gradient. Two approaches are taken:

On one setup, the mechanical resonator is a silicon nitride nanobeam with a micromagnet placed on its antinode. These nanobeams with hierarchical structure are fabricated by the Groeblacher group at TU Delft, which exhibit quality factors exceeding 10 million at 1 MHz. A single NV center inside a diamond nanopillar is brought close to the micromagnet to generate the spin-mechanical coupling. We are currently attempting to detect the backaction from a single NV (1 spin) on the mechanical motion of the nanobeam (10^12 atoms). Our most recent publication on using this platform to generate programmable entanglement between spin qubits can be found here.

On another setup, the mechanical resonator is a magnet levitated over a type-II superconductor. Pinned magnetic flux in the superconductor traps the position as well as the orientation of the magnet. The levitation approach promises not only ultra-high quality factors but also richer degrees of freedom, including rotations. By levitating micrometer-size magnets a few micrometers above the superconductor, we have measured kHz center-of mass motion and a few tens-kHz libration with quality factors exceeding 1 million. We are currently working on a new design which takes advantages of diamond membranes from High group at UChicago to circumvent several practical challenges. Read more about our work here.

[1] Rosenfeld, Emma, et al. "Efficient entanglement of spin qubits mediated by a hot mechanical oscillator." Physical Review Letters 126.25 (2021): 250505.

[2] Rabl, Peter, et al. "A quantum spin transducer based on nanoelectromechanical resonator arrays." Nature Physics 6.8 (2010): 602-608.