Talk on "Levitated Nano-Magnets as Quantum Transducers"

by Jan Gieseler; Department of Physics, Harvard University, Cambridge (USA)

Coherent coupling between a single spin degree of freedom and a massive mechanical mode is still an outstanding challenge. Such a system is highly desirable, as it would allow preparation of macroscopic quantum states of motion and it could be used to mediate an effective spin-spin interaction between distant spins. This principle is in close analogy to trapped ions that interact via collective mechanical modes, which have already demonstrated high fidelity quantum gates. One promising approach to engineer a strong spin-mechanical coupling is via magnetic field gradients. In this scheme, maximizing the spin-resonator coupling requires to employ a compliant, high quality mechanical resonator, strong magnetic field gradients, and spin qubits with very long spin coherence times. In addition, they have to be combined while preserving the excellent properties of the individual components. To address this formidable challenge, we propose a new platform based on levitated nano-magnets.

Here, we report on our experimental progress towards integrating a diamagnetically levitated micro-magnet with nitrogen-vacancy (NV) centers in diamond as a new platform for quantum applications. The absence of any support structure results in low mechanical damping and a large magnetic moment to mass ratio, thereby enabling strong coupling between the micro-magnet and nearby spins. We aim at integrating the levitated magnet with nitrogen-vacancy (NV) center defects in diamond, which will serve as the spin-qubits. The NV features optical spin read-out and initialization, microwave control, and weak coupling to the environment resulting in long spin coherence times. This hybrid setup gives controllable access to the rich (tunable) mode spectrum associated with the micro-magnet, consisting of hybridized translational, rotational and internal magnonic modes ranging from kHz all the way to GHz. When positioned nearby the levitated magnet, the NV center experiences a magnetic field that depends on the motion of the magnet. Conversely, spin flips of the electronic spin of the NV center exert forces and torques on the magnet. This leads to coupled dynamics of the magnet motion and the NV center spin. Our goal is to harness this coupling for quantum applications such as sensing, creation of macroscopic quantum states and long-range spin-spin interactions.

ESI, Schrödinger Lecture Hall, Boltzmanngasse 9a, 1090 Wien