Bruder, Christoph

Date:   Thursday, March 4, 2021
Time:   10:00
Place:   scheduled Zoom meeting
Host:    Klaus Ensslin

Quantum synchronization

Christoph Bruder
University of Basel

Synchronization of self-oscillators is a universal phenomenon that is important both in fundamental studies and in technical applications.
Experimental progress in optomechanical systems, in trapped-ion setups, and in superconducting circuit-QED architectures has motivated the study of synchronization in quantum systems. This gives rise to a number of conceptual questions, like the relation between quantum synchronization and the generation of entanglement, and leads to paradoxial phenomena like the quantum synchronization blockade [1].
Recently, we have addressed the question what is the smallest possible system that can be synchronized, using the Hilbert-space dimension as a natural measure of size. We have shown that qubits cannot be synchronized due to the lack of a limit cycle. Moving to larger spin values, we have demonstrated that a single spin 1 can be phase-locked to a weak external signal of similar frequency and exhibits all the standard features of the theory of synchronization [2]. Finally, I will report on the first experimental demonstration of quantum synchronization that we achieved by performing a digital simulation of a single spin-$1$ limit-cycle oscillator on the quantum processors of the IBM Q System [3].

[1] N. Lörch, S.E. Nigg, A. Nunnenkamp, R.P. Tiwari, and C. Bruder,
Quantum synchronization blockade: Energy quantization hinders synchronization of identical oscillators,
Phys. Rev. Lett. 118, 243602 (2017).

[2] A. Roulet and C. Bruder,
Synchronizing the smallest possible system, Phys. Rev. Lett. 121, 053601 (2018);
Quantum synchronization and entanglement generation,
Phys. Rev. Lett. 121, 063601 (2018).

[3] M. Koppenhöfer, C. Bruder, and A. Roulet,
Quantum synchronization on the IBM Q system,
Phys. Rev. Research 2, 023026 (2020).