Effect of noise on quantum circuit realization of non-Hermitian time crystals

Abstract: Non-Hermitian quantum dynamics lie in an intermediate regime between unitary Hamiltonian dynamics and trace-preserving non-unitary open quantum system dynamics. Given differences in the noise tolerance of unitary and non-unitary dynamics, it is interesting to consider implementing non-Hermitian dynamics on a noisy quantum computer. In this paper, we do so for a non-Hermitian Ising Floquet model whose many-body dynamics gives rise to persistent temporal oscillations, a form of time crystallinity. In the simplest two qubit case that we consider, there is an infinitely long-lived periodic steady state at certain fine-tuned points. These oscillations remain reasonably long-lived over a range of parameters in the ideal non-Hermitean dynamics and for the levels of noise and imperfection expected of modern day quantum devices. Using a generalized Floquet analysis, we show that infinitely long-lived oscillations are generically lost for arbitrarily weak values of common types of noise and compute corresponding damping rate. We perform simulations using IBM's Qiskit platform to confirm our findings; however, experiments on a real device (ibmq-lima) do not show remnants of these oscillations.