Abstract
Continuous-variable quantum states are of particular importance in various quantum information processing tasks including quantum communication and quantum sensing. However, a bottleneck has emerged with the fast increasing in size of the quantum systems which severely hinders their efficient characterization. In this work, we establish a systematic framework for verifying entangled continuous-variable quantum states by employing local measurements only. Our protocol is able to achieve the unconditionally high verification efficiency which is quadratically better than quantum tomography as well as other nontomographic methods. Specifically, we demonstrate the power of our protocol by showing the efficient verification of entangled two-mode and multimode coherent states with local measurements.
Highlights
Continuous-variable (CV) quantum systems have demonstrated their unique role in various quantum information processing applications [1,2]
This is the entangled coherent state, which we show how to verify
We have developed a systematic framework for verifying continuous-variable quantum states with local measurements only
Summary
Continuous-variable (CV) quantum systems have demonstrated their unique role in various quantum information processing applications [1,2]. A new characterization method called quantum state verification (QSV) has been systematically investigated in discrete-variable (DV) quantum systems [16,17]. To characterize CV quantum states, intensity measurements based on quadratures are usually employed in quantum tomography and other nontomographic methods. The intensity measurements are especially suitable for Gaussian states, as they can be fully characterized by expectation values of the quadratic operators. They are, in principle, inappropriate for the task of quantum verification since postprocessing of the experimental data is needed for estimating the quadratures. Our protocol is able to achieve the unconditionally high verification efficiency with the resource overhead given by N ∝ O( −1 ln δ−1) within infidelity and confidence level 1 − δ, which is quadratically better
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