Quantum Mechanics
http://hdl.handle.net/20.500.11824/17
2023-11-29T01:59:48ZResource-Efficient High-Dimensional Entanglement Detection via Symmetric Projections
http://hdl.handle.net/20.500.11824/1708
Resource-Efficient High-Dimensional Entanglement Detection via Symmetric Projections
Morelli, S.; Huber, M.; Tavakoli, A.
We introduce two families of criteria for detecting and quantifying the entanglement of a bipartite quantum state of arbitrary local dimension. The first is based on measurements in mutually unbiased bases and the second is based on equiangular measurements. Both criteria give a qualitative result in terms of the state's entanglement dimension and a quantitative result in terms of its fidelity with the maximally entangled state. The criteria are universally applicable since no assumptions on the state are required. Moreover, the experimenter can control the trade-off between resource-efficiency and noise-tolerance by selecting the number of measurements performed. For paradigmatic noise models, we show that only a small number of measurements are necessary to achieve nearly-optimal detection in any dimension. The number of global product projections scales only linearly in the local dimension, thus paving the way for detection and quantification of very high-dimensional entanglement.
2023-10-25T00:00:00ZCoplanar Antenna Design for Microwave Entangled Signals Propagating in Open Air
http://hdl.handle.net/20.500.11824/1655
Coplanar Antenna Design for Microwave Entangled Signals Propagating in Open Air
Gonzalez-Raya, T.; Sanz, M.
Open-air microwave quantum communication and metrology protocols must be able to transfer quantum resources from a cryostat, where they are created, to an environment dominated by thermal noise. Indeed, the states carrying such quantum resources are generated in a cryostat characterized by a temperature Tin ' 50 mK and an intrinsic impedance Zin = 50 Ω. Then, an antenna-like device is required to transfer them with minimal losses into open air, characterized by an intrinsic impedance of Zout = 377 Ω and a temperature Tout ' 300 K. This device accomplishes a smooth impedance matching between the cryostat and the open air. Here, we study the transmission of two-mode squeezed thermal states, developing a technique to design the optimal shape of a coplanar antenna to preserve the entanglement. Based on a numerical optimization procedure, we find the optimal shape of the impedance, and we propose a functional ansatz to qualitatively describe this shape. Additionally, this study reveals that the reflectivity of the antenna is very sensitive to this shape, so that small changes dramatically affect the outcoming entanglement, which could have been a limitation in previous experiments employing commercial antennae. This work is relevant in the fields of microwave quantum sensing and quantum metrology with special application to the development of the quantum radar, as well as any open-air microwave quantum communication protocol.
2022-01-01T00:00:00ZQuantum-enhanced Doppler lidar
http://hdl.handle.net/20.500.11824/1654
Quantum-enhanced Doppler lidar
Reichert, M.; Di Candia, R.; Win, M.Z.; Sanz, M.
We propose a quantum-enhanced lidar system to estimate a target’s radial velocity, which employs squeezed and frequency-entangled signal and idler beams. We compare its performance against a classical protocol using a coherent state with the same pulse duration and energy, showing that quantum resources provide a precision enhancement in the estimation of the velocity of the object. We identify three distinct parameter regimes characterized by the amount of squeezing and frequency entanglement. In two of them, a quantum advantage exceeding the standard quantum limit is achieved assuming no photon losses. Additionally, we show that an optimal measurement to attain these results in the lossless case is frequency-resolved photon counting. Finally, we consider the effect of photon losses for the high-squeezing regime, which leads to a constant factor quantum advantage higher than 3 dB in the variance of the estimator, given a roundtrip lidar-to-target-to-lidar transmissivity larger than 50%.
2022-12-01T00:00:00ZBi-Frequency Illumination: A Quantum-Enhanced Protocol
http://hdl.handle.net/20.500.11824/1653
Bi-Frequency Illumination: A Quantum-Enhanced Protocol
Casariego, M.; Omar, Y.; Sanz, M.
Quantum-enhanced, idler-free sensing protocol to measure the response of a target object to the frequency of a probe in a noisy and lossy scenario is proposed. In this protocol, a target with frequency-dependent reflectivity (Formula presented.) embedded in a thermal bath is considered. The aim is to estimate the parameter (Formula presented.), since it contains relevant information for different problems. For this, a bi-frequency quantum state is employed as the resource, since it is necessary to capture the relevant information about the parameter. Computing the quantum Fisher information H relative to the parameter λ in an assumed neighborhood of (Formula presented.) for a two-mode squeezed state ((Formula presented.)), and a pair of coherent states ((Formula presented.)), a quantum enhancement is shown in the estimation of λ. This quantum enhancement grows with the mean reflectivity of the probed object, and is noise-resilient. Explicit formulas are derived for the optimal observables, and an experimental scheme based on elementary quantum optical transformations is proposed. Furthermore, this work opens the way to applications in both radar and medical imaging, in particular in the microwave domain.
2022-11-01T00:00:00Z