Experimental Characterization of Unsharp Qubit Observables and Sequential Measurement Incompatibility via Quantum Random Access Codes

Anwer, Hammad; Muhammad, Sadiq; Cherifi, Walid; Miklin, Nikolai; Tavakoli, Armin; Bourennane, Mohamed

doi:10.1103/physrevlett.125.080403

Cited by 61 publications

(53 citation statements)

References 44 publications

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“…Recently, it has been exploited for sequential protocols, in which a system undergoes multiple measurements without ever completely collapsing or losing its useful quantum features, which can be harvested repeatedly. In this manner, Bell inequalities can be violated more times [36][37][38][39][40], quantum random access codes can be used by two parties [41,42], and quantum instruments can be tested [43]. More important for this work is using weak measurements to produce random bits from the same physical system repeatedly [44,45].…”

Section: Introductionmentioning

confidence: 99%

Experimental test of sequential weak measurements for certified quantum randomness extraction

et al. 2021

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Quantum nonlocality offers a secure way to produce random numbers: Their unpredictability is intrinsic and can be certified just by observing the statistic of the measurement outcomes, without assumptions on how they are produced. To do this, entangled pairs are generated and measured to violate a Bell inequality with the outcome statistics. However, after a projective quantum measurement, entanglement is entirely destroyed and cannot be used again. This fact poses an upper bound to the amount of randomness that can be produced from each quantum state when projective measurements are employed. Instead, by using weak measurements, some entanglement can be maintained and reutilized, and a sequence of weak measurements can extract an unbounded amount of randomness from a single state as predicted in Phys. Rev. A 95, 020102(R) (2017). We study the feasibility of these weak measurements, analyze the robustness to imperfections in the quantum state they are applied to, and then test them using an optical setup based on polarization-entangled photon pairs. We show that the weak measurements are realizable, but can improve the performance of randomness generation only in close-to-ideal conditions.

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Section: Introductionmentioning

confidence: 99%

Experimental test of sequential weak measurements for certified quantum randomness extraction

et al. 2021

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“…This has also been experimentally demonstrated [10,11]. Moreover, shared quantum correlations have recently also been studied in other tasks such as entanglement witnessing [12], quantum steering [13,14] and a semidevice-independent setting [15][16][17][18].…”

Section: Introductionmentioning

confidence: 84%

Noise-robust preparation contextuality shared between any number of observers via unsharp measurements

Anwer

Wilson

Silva

et al. 2021

Quantum

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Multiple observers who independently harvest nonclassical correlations from a single physical system share the system's ability to enable quantum correlations. We show that any number of independent observers can share the preparation contextual outcome statistics enabled by state ensembles in quantum theory. Furthermore, we show that even in the presence of any amount of white noise, there exists quantum ensembles that enable such shared preparation contextuality. The findings are experimentally realised by applying sequential unsharp measurements to an optical qubit ensemble which reveals three shared demonstrations of preparation contextuality.

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“…On the other hand, in order to implement the phase diffusion, we add a random phase that is different for each pixel. In particular, we use a random function consisting in a flat distribution between the two values − /2 and /2, so that the mixing factors α and β of the noisy measurements (20) are functions of . Finally, we use a second HWP and a polarizer (P) with axis on the horizontal direction to complete the projection stage.…”

Section: A Experimental Apparatusmentioning

confidence: 99%

“…The realization of experiments aimed at testing and assessing quantum incompatibility is a very novel field of research, to the point that, up to our knowledge, only two recent articles addressed this topic before the present one. In [20], the degree of incompatibility of two qubit measurements was evaluated by determining the success probability of a communication protocol based on random access code. In the proposed experiment, incompatibility was detected and quantified by means of the violation of a classical bound in the quantum version of the protocol [21].…”

Section: Introductionmentioning

confidence: 99%

Experimentally determining the incompatibility of two qubit measurements

Smirne,

Cialdi,

Cipriani

et al. 2021

Preprint

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We describe and realize an experimental procedure for assessing the incompatibility of two qubit measurements. The experiment consists in a state discrimination task where either measurement is used according to some partial intermediate information. The success statistics of the task provides an upper bound for the amount of incompatibility of the two measurements, as it is quantified by means of their incompatibility robustness. For a broad class of unbiased and possibly noisy qubit measurements, one can make this upper bound coincide with the true value of the robustness by suitably tuning the preparation of the experiment. We demonstrate this fact in an optical setup, where the qubit states are encoded into the photons' polarization degrees of freedom, and incompatibility is directly accessed by virtue of a refined control on the amplitude, phase and purity of the final projection stage of the measurements. Our work thus establishes the practical feasibility of a recently proposed method for the detection of quantum incompatibility.

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Experimental Characterization of Unsharp Qubit Observables and Sequential Measurement Incompatibility via Quantum Random Access Codes

Cited by 61 publications

References 44 publications

Experimental test of sequential weak measurements for certified quantum randomness extraction

Experimental test of sequential weak measurements for certified quantum randomness extraction

Noise-robust preparation contextuality shared between any number of observers via unsharp measurements

Experimentally determining the incompatibility of two qubit measurements

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