Talks

Exploring continuous time crystals (CTCs) within the symmetric subspace of spin systems has been a subject of intensive research in recent times. Thus far, the stability of the time-crystal phase outside the symmetric subspace in such spin systems has gone largely unexplored. Here, I present results relating the effect of including the asymmetric subspaces on the dynamics of CTCs in a driven dissipative spin model. This results in multistability, and the dynamics becomes dependent on the initial state. Remarkably, this multistability leads to exotic synchronization regimes such as chimera states and cluster synchronization in an ensemble of coupled identical CTCs. Interestingly, it leads to other nonlinear phenomena such as oscillation death and signature of chaos.

(based on work with coauthors reported in Phys. Rev. Lett. 133, 260403, 2024)

Quantum measurements give rise to back-action on the measured system. Tuning the quantum measurement dynamics, and repeating the measurement protocol irrespective of the detectors’ readouts, may be employed to engineer a stable target state. Such a scheme is referred to as a passive quantum steering protocol. The ground state of a given Hamiltonian may or may not be steerable, depending on whether the Hamiltonian is non-frustrated or frustrated. We will discuss how cooling to the ground state may be facilitated even when acting on (measuring) small parts of the system ( “dilute cooling”).
We will also discuss how close to the ground state one can get in the presence of non-steerable frustrated Hamiltonians.

Spin ensembles are promising quantum technological platforms, but their utility relies on the ability to perform quantum error correction (QEC) for decoherences in these systems. Typical QEC for ensembles requires addressing individually resolved qubits, but this is practically challenging in most realistic architectures. Here, we propose QEC schemes for unresolvable spin ensembles. By using degenerate superpositions of excited states, which are fundamentally mixed, we find codes that can protect against both individual and collective errors, including dephasing, decay, and pumping. We show how information recovery can be achieved with only collective measurement and control, and illustrate its applications in extending memory lifetime and loss-tolerant sensing.

We investigate the thermodynamic uncertainty relation (TUR), i.e., a trade-off between entropy production rate and relative power fluctuations, for nondegenerate three-level and degenerate four-level maser heat engines. In the nondegenerate case, we consider two slightly different configurations of the three-level maser heat engine and contrast their degree of violation of the standard TUR. We associate their different TUR-violating properties to the phenomenon of spontaneous emission, which gives rise to an asymmetry between them. Furthermore, in the high-temperature limit, we show that the standard TUR relation is always violated for both configurations. For the degenerate four-level engine, we study the effects of noise-induced coherence on the TUR. We show that, depending on the parametric regime of operation, noise-induced coherence can either suppress or amplify the relative power fluctuations.