Direct Measurement of a Nonlocal Entangled Quantum State

Pan, Weiwei; Xu, Xiao‐Ye; Kedem, Yaron; Wang, Qinqin; Chen, Zhe; Jan, Munsif; Sun, Kai; Xu, Jin‐Shi; Han, Yong‐Jian; Li, Chuan‐Feng; Guo, Guang-Can

doi:10.1103/physrevlett.123.150402

Cited by 62 publications

(43 citation statements)

References 42 publications

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“…Recent advances have given affirmative answers. For instance, in the work of directly measuring an entangled biphoton state 28 , the authors read out the required weak values of non-local observables via strong measurements and the concept of modular value 29 . Besides, a linear relationship exists between the probability of successful post-selection and the strength of a unitary perturbation.…”

Section: Resultsmentioning

confidence: 99%

Experimental exchange of grins between quantum Cheshire cats

Liu

Pan

et al. 2020

Nat Commun

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Intuition suggests that an object should carry all of its physical properties. However, a quantum object may not act in such a manner-it can temporarily leave some of its physical properties where it never appears. This phenomenon is known as the quantum Cheshire cat effect. It has been proposed that a quantum object can even permanently discard a physical property and obtain a new one it did not initially have. Here, we observe this effect experimentally by casting non-unitary imaginary-time evolution on a photonic cluster state to extract weak values, which reveals the counterintuitive phenomenon that two photons exchange their spins without classically meeting each other. A phenomenon presenting only in the quantum realm, our results are in stark contrast with the perception of inseparability between objects and properties, and shed new light on comprehension of the ontology of observables.

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Section: Resultsmentioning

confidence: 99%

Experimental exchange of grins between quantum Cheshire cats

Liu

Pan

et al. 2020

Nat Commun

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“…While more ingenious strategies may exist, an experimental measurement of the wave function itself (using, e.g., techniques developed in Refs. [41][42][43][44]) can in principle be used to reconstruct the Husimi distribution.…”

Section: Discussionmentioning

confidence: 99%

On the experiment-friendly formulation of quantum backflow

Barbier

Goussev

2021

Quantum

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In its standard formulation, quantum backflow is a classically impossible phenomenon in which a free quantum particle in a positive-momentum state exhibits a negative probability current. Recently, Miller et al. [Quantum 5, 379 (2021)] have put forward a new, "experiment-friendly" formulation of quantum backflow that aims at extending the notion of quantum backflow to situations in which the particle's state may have both positive and negative momenta. Here, we investigate how the experiment-friendly formulation of quantum backflow compares to the standard one when applied to a free particle in a positive-momentum state. We show that the two formulations are not always compatible. We further identify a parametric regime in which the two formulations appear to be in qualitative agreement with one another.

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“…As our technique largely preserves the initial quantum state, potential applications include demonstrating contextuality [48][49][50][51], and tests of Leggett-Garg inequalities [33,[52][53][54][55][56][57]. Motivated by the direct measurement of entangled systems [58,59] and entanglement witnesses [60,61], a potential future research direction is the use of this technique for characterizing entanglement.…”

Section: Discussionmentioning

confidence: 99%

Theory and experiment for resource-efficient joint weak-measurement

Martinez-Becerril

Bussières

Curic

et al. 2021

Quantum

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Incompatible observables underlie pillars of quantum physics such as contextuality and entanglement. The Heisenberg uncertainty principle is a fundamental limitation on the measurement of the product of incompatible observables, a 'joint' measurement. However, recently a method using weak measurement has experimentally demonstrated joint measurement. This method [Lundeen, J. S., and Bamber, C. Phys. Rev. Lett. 108, 070402, 2012] delivers the standard expectation value of the product of observables, even if they are incompatible. A drawback of this method is that it requires coupling each observable to a distinct degree of freedom (DOF), i.e., a disjoint Hilbert space. Typically, this 'read-out' system is an unused internal DOF of the measured particle. Unfortunately, one quickly runs out of internal DOFs, which limits the number of observables and types of measurements one can make. To address this limitation, we propose and experimentally demonstrate a technique to perform a joint weak-measurement of two incompatible observables using only one DOF as a read-out system. We apply our scheme to directly measure the density matrix of photon polarization states.

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Direct Measurement of a Nonlocal Entangled Quantum State

Cited by 62 publications

References 42 publications

Experimental exchange of grins between quantum Cheshire cats

Experimental exchange of grins between quantum Cheshire cats

On the experiment-friendly formulation of quantum backflow

Theory and experiment for resource-efficient joint weak-measurement

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