| 1. |
- Bakhshinezhad, Pharnam, et al.
(författare)
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Scalable Entanglement Certification via Quantum Communication
- 2024
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Ingår i: PRX Quantum. - 2691-3399. ; 5:2
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Tidskriftsartikel (refereegranskat)abstract
- Harnessing the advantages of shared entanglement for sending quantum messages often requires the implementation of complex two-particle entangled measurements. We investigate entanglement advantages in protocols that use only the simplest two-particle measurements, namely, product measurements. For experiments in which only the dimension of the message is known, we show that robust entanglement advantages are possible but that they are fundamentally limited by Einstein-Podolsky-Rosen steering. Subsequently, we propose a natural extension of the standard scenario for these experiments and show that it circumvents this limitation. This leads us to prove entanglement advantages from every entangled two-qubit Werner state, evidence its generalization to high-dimensional systems, and establish a connection to quantum teleportation. Our results reveal the power of product measurements for generating quantum correlations in entanglement-assisted communication and they pave the way for practical semi-device-independent entanglement certification well beyond the constraints of Einstein-Podolsky-Rosen steering.
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| 2. |
- Bakhshinezhad, Pharnam, et al.
(författare)
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Trade-offs between precision and fluctuations in charging finite-dimensional quantum batteries
- 2024
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Ingår i: Physical Review E. - 2470-0045. ; 109:1
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Tidskriftsartikel (refereegranskat)abstract
- Within quantum thermodynamics, many tasks are modeled by processes that require work sources represented by out-of-equilibrium quantum systems, often dubbed quantum batteries, in which work can be deposited or from which work can be extracted. Here we consider quantum batteries modeled as finite-dimensional quantum systems initially in thermal equilibrium that are charged via cyclic Hamiltonian processes. We present optimal or near-optimal protocols for N identical two-level systems and individual d-level systems with equally spaced energy gaps in terms of the charging precision and work fluctuations during the charging process. We analyze the trade-off between these figures of merit as well as the performance of local and global operations.
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| 3. |
- Boeyens, Julia, et al.
(författare)
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Probe thermometry with continuous measurements
- 2023
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Ingår i: New Journal of Physics. - 1367-2630. ; 25:12
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Tidskriftsartikel (refereegranskat)abstract
- Temperature estimation plays a vital role across natural sciences. A standard approach is provided by probe thermometry, where a probe is brought into contact with the sample and examined after a certain amount of time has passed. In situations where, for example, preparation of the probe is non-trivial or total measurement time of the experiment is the main resource that must be optimized, continuously monitoring the probe may be preferred. Here, we consider a minimal model, where the probe is provided by a two-level system coupled to a thermal reservoir. Monitoring thermally activated transitions enables real-time estimation of temperature with increasing accuracy over time. Within this framework we comprehensively investigate thermometry in both bosonic and fermionic environments employing a Bayesian approach. Furthermore, we explore adaptive strategies and find a significant improvement on the precision. Additionally, we examine the impact of noise and find that adaptive strategies may suffer more than non-adaptive ones for short observation times. While our main focus is on thermometry, our results are easily extended to the estimation of other environmental parameters, such as chemical potentials and transition rates.
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| 4. |
- Francesco Diotallevi, Giovanni, et al.
(författare)
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Steady-state entanglement production in a quantum thermal machine with continuous feedback control
- 2024
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Ingår i: New Journal of Physics. - 1367-2630. ; 26:5
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Tidskriftsartikel (refereegranskat)abstract
- Quantum thermal machines can generate steady-state entanglement by harvesting spontaneous interactions with local environments. However, using minimal resources and control, the entanglement is typically weak. Here, we study entanglement generation in a two-qubit quantum thermal machine in the presence of a continuous feedback protocol. Each qubit is measured continuously and the outcomes are used for real-time feedback to control the local system-environment interactions. We show that there exists an ideal operation regime where the quality of entanglement is significantly improved, to the extent that it can violate standard Bell inequalities and uphold quantum teleportation. In agreement with (Khandelwal et al 2020 New J. Phys. 22 073039), we also find, for ideal operation, that the heat current across the system is proportional to the entanglement concurrence. Finally, we investigate the robustness of entanglement production when the machine operates away from the ideal conditions.
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| 5. |
- Lipka-Bartosik, Patryk, et al.
(författare)
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Fundamental Limits on Anomalous Energy Flows in Correlated Quantum Systems
- 2024
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Ingår i: Physical Review Letters. - 0031-9007. ; 132:14
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Tidskriftsartikel (refereegranskat)abstract
- In classical thermodynamics energy always flows from the hotter system to the colder one. However, if these systems are initially correlated, the energy flow can reverse, making the cold system colder and the hot system hotter. This intriguing phenomenon is called "anomalous energy flow"and shows the importance of initial correlations in determining physical properties of thermodynamic systems. Here we investigate the fundamental limits of this effect. Specifically, we find the optimal amount of energy that can be transferred between quantum systems under closed and reversible dynamics, which then allows us to characterize the anomalous energy flow. We then explore a more general scenario where the energy flow is mediated by an ancillary quantum system that acts as a catalyst. We show that this approach allows for exploiting previously inaccessible types of correlations, ultimately resulting in an energy transfer that surpasses our fundamental bound. To demonstrate these findings, we use a well-studied quantum optics setup involving two atoms coupled to an optical cavity.
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