Hinarejos, M., Bañuls, M. C., & Perez, A. (2013). A Study of Wigner Functions for Discrete-Time Quantum Walks. J. Comput. Theor. Nanosci., 10(7), 1626–1633.
Abstract: We perform a systematic study of the discrete time Quantum Walk on one dimension using Wigner functions, which are generalized to include the chirality (or coin) degree of freedom. In particular, we analyze the evolution of the negative volume in phase space, as a function of time, for different initial states. This negativity can be used to quantify the degree of departure of the system from a classical state. We also relate this quantity to the entanglement between the coin and walker subspaces.
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Araujo Filho, A. A., Hassanabadi, H., Reis, J. A. A. S., & Lisboa-Santos, L. (2023). Thermodynamics of a quantum ring modified by Lorentz violation. Phys. Scr., 98(6), 065943–13pp.
Abstract: In this work, we investigate the consequences of Lorentz-violating terms in the thermodynamic properties of a 1-dimensional quantum ring. In particular, we use the ensemble theory to obtain our results of interest. The thermodynamic functions as well as the spin currents are calculated as a function of the temperature. We observe that parameter xi, which triggers the Lorentz symmetry breaking, plays a major role in low temperature regime. Finally, depending on the configuration of the system, electrons can rotate in two different directions: clockwise and counterclockwise.
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Biagi, N., Francesconi, S., Gessner, M., Bellini, M., & Zavatta, A. (2022). Remote Phase Sensing by Coherent Single Photon Addition. Adv. Quantum Technol., 5(12), 2200039–9pp.
Abstract: A remote phase sensing scheme is proposed, inspired by the high sensitivity of the entanglement produced by coherent multimode photon addition on the phase set in the remote heralding apparatus. By exploring the case of delocalized photon addition over two modes containing identical coherent states, the optimal observable to perform remote phase estimation from heralded quadrature measurements is derived. The technique is experimentally tested with calibration measurements and then used for estimating a remote phase with a sensitivity that is found to scale with the intensity of the local coherent states, which never interacted with the sample.
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Sorelli, G., Gessner, M., Treps, N., & Walschaers, M. (2024). Gaussian quantum metrology for mode-encoded parameters. New J. Phys., 26(7), 073022–23pp.
Abstract: Quantum optical metrology aims to identify ultimate sensitivity bounds for the estimation of parameters encoded into quantum states of the electromagnetic field. In many practical applications, including imaging, microscopy, and remote sensing, the parameter of interest is not only encoded in the quantum state of the field, but also in its spatio-temporal distribution, i.e. in its mode structure. In this mode-encoded parameter estimation setting, we derive an analytical expression for the quantum Fisher information valid for arbitrary multimode Gaussian fields. To illustrate the power of our approach, we apply our results to the estimation of the transverse displacement of a beam and to the temporal separation between two pulses. For these examples, we show how the estimation sensitivity can be enhanced by adding squeezing into specific modes.
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Fadel, M., Yadin, B., Mao, Y. P., Byrnes, T., & Gessner, M. (2023). Multiparameter quantum metrology and mode entanglement with spatially split nonclassical spin ensembles. New J. Phys., 25(7), 073006–25pp.
Abstract: We identify the multiparameter sensitivity of entangled spin states, such as spin-squeezed and Dicke states that are spatially distributed into several addressable spatial modes. Analytical expressions for the spin-squeezing matrix of families of states that are accessible by current atomic experiments reveal the quantum gain in multiparameter metrology, as well as the optimal strategies to maximize the sensitivity gain for the estimation of any linear combination of parameters. We further study the mode entanglement of these states by deriving a witness for genuine k-partite mode entanglement from the spin-squeezing matrix. Our results highlight the advantage of mode entanglement for distributed sensing, and outline optimal protocols for multiparameter estimation with nonclassical spatially-distributed spin ensembles. We illustrate our findings with the design of a protocol for gradient sensing with a Bose-Einstein condensate in an entangled spin state in two modes.
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