- Quantum coherence enables hybrid multitask and multisource regimes in
autonomous thermal machinesby Kenza Hammam on August 30, 2023 at 3:12 pm
Non-equilibrium effects may have a profound impact on the performance of thermal devices performing thermodynamic tasks such as refrigeration or heat pumping. The possibility of enhancing the […]

- Thermodynamics of hybrid quantum rotor devicesby Heather Leitch on April 17, 2023 at 10:00 am
We investigate the thermodynamics of a hybrid quantum device consisting of two qubits collectively interacting with a quantum rotor and coupled dissipatively to two equilibrium reservoirs at […]

- Thermodynamics of coupled time crystals with an application to energy
storageby Paulo J. Paulino on November 7, 2024 at 4:21 pm
Open many-body quantum systems can exhibit intriguing nonequilibrium phases of matter, such as time crystals. In these phases, the state of the system spontaneously breaks the time-translation symmetry of the dynamical generator, which typically manifests through persistent oscillations of an order parameter. A paradigmatic model displaying such a symmetry breaking is the boundary time crystal, which has been extensively analyzed experimentally and theoretically. Despite the broad interest in these nonequilibrium phases, their thermodynamics and their fluctuating behavior remain largely unexplored, in particular for the case of coupled time crystals. In this work, we consider two interacting boundary time crystals and derive a consistent interpretation of their thermodynamic behavior. We fully characterize their average dynamics and the behavior of their quantum fluctuations, which allows us to demonstrate the presence of quantum and classical correlations in both the stationary and the time-crystal phases displayed by the system. We furthermore exploit our theoretical derivation to explore possible applications of time crystals as quantum batteries, demonstrating their ability to efficiently store energy.

- Assessing non-Gaussian quantum state conversion with the stellar rankby Oliver Hahn on October 31, 2024 at 8:13 am
State conversion is a fundamental task in quantum information processing. Quantum resource theories allow to analyze and bound conversions that use restricted sets of operations. In the context of continuous-variable systems, state conversions restricted to Gaussian operations are crucial for both fundamental and practical reasons -- particularly in state preparation and quantum computing with bosonic codes. However, previous analysis did not consider the relevant case of approximate state conversion. In this work, we introduce a framework for assessing approximate Gaussian state conversion by extending the stellar rank to the approximate stellar rank, which serves as an operational measure of non-Gaussianity. We derive bounds for Gaussian state conversion under both approximate and probabilistic conditions, yielding new no-go results for non-Gaussian state preparation and enabling a reliable assessment of the performance of generic Gaussian conversion protocols.

- Qubit magic-breaking channelsby Ayan Patra on September 6, 2024 at 5:37 pm
We develop a notion of quantum channels that can make states useless for universal quantum computation by destroying their magic (non-stabilizerness) - we refer to them as magic-breaking channels. We establish the properties of these channels in arbitrary dimensions. We prove the necessary and sufficient criteria for qubit channels to be magic-breaking and present an algorithm for determining the same. Moreover, we provide compact criteria in terms of the parameters for several classes of qubit channels to be magic-breaking under various post-processing operations. Further, we investigate the necessary and sufficient conditions for the tensor product of multiple qubit channels to be magic-breaking. We establish implications of the same for the dynamical resource theory of magic preservability.

- Coherent expansion of the motional state of a massive nanoparticle
beyond its linear dimensionsby R. Muffato on August 18, 2024 at 9:11 pm
Quantum mechanics predicts that massive particles exhibit wave-like behavior. Matterwave interferometry has been able to validate such predictions through ground-breaking experiments involving microscopic systems like atoms and molecules. The wavefunction of such systems coherently extends over a distance much larger than their size, an achievement that is incredibly challenging for massive and more complex objects. Yet, reaching similar level of coherent diffusion will enable tests of fundamental physics at the genuinely macroscopic scale, as well as the development of quantum sensing apparata of great sensitivity. We report on experimentally achieving an unprecedented degree of position diffusion in a massive levitated optomechanical system through frequency modulation of the trapping potential. By starting with a pre-cooled state of motion and employing a train of sudden pulses yet of mild modulation depth, we surpass previously attained values of position diffusion in this class of systems to reach diffusion lengths that exceed the physical dimensions of the trapped nanoparticle.

- Critical assessment of information back-flow in measurement-free
teleportationby Hannah McAleese on August 15, 2024 at 1:59 pm
We assess a scheme for measurement-free quantum teleportation from the perspective of the resources underpinning its performance. In particular, we focus on recently made claims about the crucial role played by the degree of non-Markovianity of the dynamics of the information carrier whose state we aim to teleport. We prove that any link between efficiency of teleportation and back-flow of information depends fundamentally on the way the various operations entailed by the measurement-free teleportation protocol are implemented, while - in general - no claim of causal link can be made. Our result reinforces the need for the explicit assessment of the underlying physical platform when assessing the performance and resources for a given quantum protocol and the need for a rigorous quantum resource theory of non-Markovianity.

- Distributing quantum correlations through local operations and classical
resourcesby Adam G. Hawkins on August 10, 2024 at 8:42 am
Distributing quantum correlations to each node of a network is a key aspect of quantum networking. Here, we present a robust, physically-motivated protocol by which global quantum correlations, as characterised by the discord, can be distributed to quantum memories using a mixed state of information carriers which possess only classical correlations. In addition to this, said distribution is measurement-outcome independent, and the distribution is done using only bilocal unitary operations and projective measurements. We also explore the scaling of this protocol for larger networks and illustrate the structure of the quantum correlations, showing its dependence on the local operations performed.

- Information flow-enhanced precision in collisional quantum thermometryby Taysa M. Mendonça on July 31, 2024 at 2:09 pm
We describe and analyze a quantum thermometer based on a multi-layered collisional model. The proposed architecture provides significant sensitivity even for short interaction times between the ancillae comprised in the thermometer and the system to be probed, and a small number of information-acquiring collisions. The assessment of the flow of information taking place within the layered thermometer and between system and thermometer reveals that the tuning of the mutual backflow of information has a positive influence on the precision of thermometry, and helps unveiling the information-theoretic mechanisms behind the working principles of the proposed architecture.

- Generating quantum non-local entanglement with mechanical rotationsby Marko Toroš on July 19, 2024 at 12:56 pm
Recent experiments have searched for evidence of the impact of non-inertial motion on the entanglement of particles. The success of these endeavours has been hindered by the fact that such tests were performed within spatial scales that were only "local" when compared to the spatial scales over which the non-inertial motion was taking place. We propose a Sagnac-like interferometer that, by challenging such bottlenecks, is able to achieve entangled states through a mechanism induced by the mechanical rotation of a photonic interferometer. The resulting states violate the Bell-Clauser-Horne-Shimony-Holt (CHSH) inequality all the way up to the Tsirelson bound, thus signaling strong quantum nonlocality. Our results demonstrate that mechanical rotation can be thought of as resource for controlling quantum non-locality with implications also for recent proposals for experiments that can probe the quantum nature of curved spacetimes and non-inertial motion.

- Criticality-amplified quantum probing of a spontaneous collapse modelby Giorgio Zicari on July 12, 2024 at 2:37 pm
Spontaneous collapse models, which are phenomenological mechanisms introduced and designed to account for dynamical wavepacket reduction, are attracting a growing interest from the community interested in the characterisation of the quantum-to-classical transition. Here, we introduce a {\it quantum-probing} approach to the quest of deriving metrological upper bounds on the free parameters of such empirical models. To illustrate our approach, we consider an extended quantum Ising chain whose elements are -- either individually or collectively -- affected by a mechanism responsible for spontaneous collapse. We explore configurations involving out-of-equilibrium states of the chain, which allows us to infer information about the collapse mechanism before it is completely scrambled from the state of the system. Moreover, we investigate potential amplification effects on the probing performance based on the exploitation of quantum criticality.

- On the effectiveness of the collapse in the Diósi-Penrose modelby Laria Figurato on June 26, 2024 at 4:57 pm
The possibility that gravity plays a role in the collapse of the quantum wave function has been considered in the literature, and it is of relevance not only because it would provide a solution to the measurement problem in quantum theory, but also because it would give a new and unexpected twist to the search for a unified theory of quantum and gravitational phenomena, possibly overcoming the current impasse. The Di\'osi-Penrose model is the most popular incarnation of this idea. It predicts a progressive breakdown of quantum superpositions when the mass of the system increases; as such, it is susceptible to experimental verification. Current experiments set a lower bound $R_0\gtrsim 4 \times 10^{-10}$ m for the free parameter of the model, excluding some versions of it. In this work we search for an upper bound, coming from the request that the collapse is effective enough to guarantee classicality at the macroscopic scale: we find out that not all macroscopic systems collapse effectively. If one relaxes this request, a reasonable (although to some degree arbitrary) bound is found to be: $R_0\lesssim 10^{-4}$ m. This will serve to better direct future experiments to further test the model.