
Quantum Information and Many-Body Physics
• Atominstitut TU Wien •
Research Topics
Quantum Thermal Machines A modern challenge of quantum technology is to develop control over quantum systems, to make them capable of simulating interesting non-equilibrium physics, otherwise impossible to study with classical simulations. In this context, our approach is to consider a thermodynamic-like setup, and investigate simple primitive operations, like compression/expansion or splitting/merging, designed to be implementable in state-of-art experiments with quantum gases. This way, we aim to significantly advance the state-of-art experiments with quantum gases, e.g., challenging the current limits for cooling, producing in a controlled way quantum-correlation-driven phase transitions and so on. At the same time, the methods we aim to build up, being fully developed in a realistically-implementable and non-equilibrium regime, will force us to reconsider and upgrade the machinery of quantum thermodynamics.
Fig: Science 360 416–418 (2018), credit to Iagoba Apellaniz
Entanglement and metrology in many-body physics From a quantum foundational viewpoint, a big question stands: how far in the macroscopic regime can we witness quantum effects? A common intuition is that at large scales decoherence inevitably erases quantum effects. In this respect, to make more precise quantitative statements, it is very helpful to link more and more deeply the physics of quantum many-body systems with concepts like entanglement. In particular, we follow an approach based on entanglement witnesses, like spin-squeezing inequalities, that have been proven very successful, also with respect to the experimental implementation, especially in atomic gases. In parallel, as an application of such many-body entangled states we investigate the problem of estimating a parameter with quantum resources with the idea of focusing on the concrete task of frequency/time estimation. This choice is dictated by the fact that especially in the case of clocks the most precise current standards, i.e., atomic clocks, still do not make use of any quantum “resource”, which clashes with theoretical quantum protocols that could in principle overcome classical limits.
Temporal Quantum Correlations In dynamical non-equilibrium situations there is not just entanglement that plays a fundamental role. As noted already by Heisenberg, measurements of “complementary” observables are incompatible, which means that one necessarily disturbs the other if performed in a sequence. In this case it is perhaps even more counter-intuitive the fact that this incompatibility can be also seen as a resource for generating temporal sequences of outputs, like bit strings. This resource can be quantified in terms of the minimal number of distinguishable states available to a machine, which is a notion of memory. Furthermore, there is a distinction if these states can be manipulated via a classical finite-state machine or a quantum one, which calls for the question: what is the classical memory-cost of simulating a quantum finite-state machine? This can be quantified by looking at nontrivial bounds for the probability of generating complex sequences. In this framework, we look also for connections between different quantifications of temporal correlations, like non-Markovianity or error-disturbance trade-offs, which also relate to foundational questions such as the existence of extensions of so-called Macro-realist models for simulating quantum temporal sequences.
Funding: