Rotating Quantum Stuff

Speaker: Professor Andy Martin
Affiliation: University of Melbourne

Abstract

In this talk I will focus on our recent work on rotating quantum stuff. The “stuff” in question is nitrogen-vacancy defects in diamond (experiment) and dipolar Bose-Einstein condensates (theory). In general rotation and rotational symmetries are at the heart of quantum mechanics, but physical rotation is typically slow compared to quantum time scales that manipulating and measuring quantum effects for a rotating quantum system is challenging. We have demonstrated the ability to do just that with nitrogen-vacancy qubits in diamond. We spin these qubits at up to 500,000 rpm, so fast that the qubit can make a complete rotation while maintaining quantum coherence, at room temperature. During a rotation, a single qubit can be initialized into a known superposition and its quantum state can be manipulated and read out. In the first half of this talk I will present our results, focusing on the detection of rotationally induced pseudo-fields, and the use of rotation to improve the sensitivity of nitrogen-vacancy sensors to static magnetic fields [1,2].

The second half of this talk will focus on a new [3] way to generate vortices in dipolar Bose-Einstein condensate, through the rotation of the magnetic field aligning the dipoles in the condensate. When a dipolar Bose-Einstein condensate (dBEC) is subjected to a rotating dipole aligning magnetic field, the resulting precession of the dipole moments of a magnetic dipolar Bose-Einstein condensate (dBEC) imparts angular momentum to the system. Due to the superfluidity of an interacting BEC, this has the consequence of quantum vortices forming in a hitherto vorticity-free fluid. Our recent work [4] focusses on theoretically tracking the evolution of a dBEC as the magnetic field rotation frequency is slowly accelerated from zero until the vortices have formed, and then observing the relaxation of the system to its final state at a fixed rotation frequency. We find that the dBEC closely follows pre-existing semi-analytical predictions until the onset of vorticity, and that the vortex-filled states are characterised by background density striping and tilting. After sufficiently long hold durations, the vortices relax into an Abrikosov lattice with the lattice and background dBEC density profile approaching our predictions of the expected ground state. These theoretical findings provide a complementary perspective on the recent realisation of vortices in dBECs via dipole rotation [3].

References:

[1] A.A. Wood, A.G. Aeppli, E. Lilette, Y.Y. Fein, A. Stacey, L.C.L. Hollenberg, R.E. Scholten and A.M. Martin, Physical Review B 98, 174114 (2018).
[2] A.A. Wood, A. Stacey and A.M. Martin, arXiv:2203.14230 (2022) (Accepted for publication in Physical Review Applied)
[3] L. Klaus, T. Bland, E. Poli, C. Politi, G. Lamporesi, E. Casotti, R.N. Bisset, M.J. Mark and F. Ferlaino, arXiv:2206.12265
[4] S.B. Prasad, T. Bland, B.C. Mulkerin, N.G. Parker and A.M. Martin, Physical Review A 100, 023625 (2019)