Challenging preconceptions about Bell tests with photon pairs

Vivoli, Valentina Caprara; Sekatski, Pavel; Bancal, Jean-Daniel; Lim, Charles Ci Wen; Christensen, Barbara L.; Martin, Anthony; Thew, Rob; Zbinden, Hugo; Gisin, Nicolas; Sangouard, Nicolas

doi:10.1103/physreva.91.012107

Cited by 24 publications

(26 citation statements)

References 22 publications

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“…The overall detection efficiencies at Alice and Bob are thus given by η D and η D η T , respectively. Recent results by CapraraVivoli et al [30] have shown that a loophole-free test of the CHSH inequality in (1) based on the deterministic strategy described above requires an overall detection efficiency, which is at least 2/3 to exhibit a value of S > 2. Assuming ideal fiber coupling and detectors at both parties (i.e., η D = 1), this corresponds to a distance of 8.8km for the optical fiber communication channel to Bob (α = 0.2dB/km attenuation).…”

Section: B Entanglement-swapping Relay-assisted Diqkdmentioning

confidence: 99%

Progress towards practical device-independent quantum key distribution with spontaneous parametric down-conversion sources, on-off photodetectors, and entanglement swapping

Seshadreesan¹,

Takeoka²,

Sasaki³

2016

Phys. Rev. A

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Device-independent quantum key distribution (DIQKD) guarantees unconditional security of secret key without making assumptions about the internal workings of the devices used. It does so using the loophole-free violation of a Bell's inequality. The primary challenge in realizing DIQKD in practice is the detection loophole problem that is inherent to photonic tests of Bell's inequalities over lossy channels. We revisit the proposal of Curty and Moroder [Phys. Rev. A 84, 010304(R) (2011)] to use a linear optics-based entanglementswapping relay (ESR) to counter this problem. We consider realistic models for the entanglement sources and photodetectors; more precisely, (a) polarization-entangled states based on pulsed spontaneous parametric downconversion (SPDC) sources with infinitely higher order multi-photon components and multimode spectral structure, and (b) on-off photodetectors with non-unit efficiencies and non-zero dark count probabilities. We show that the ESR-based scheme is robust against the above imperfections and enables positive key rates at distances much larger than what is possible otherwise.

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Section: B Entanglement-swapping Relay-assisted Diqkdmentioning

confidence: 99%

Progress towards practical device-independent quantum key distribution with spontaneous parametric down-conversion sources, on-off photodetectors, and entanglement swapping

Seshadreesan¹,

Takeoka²,

Sasaki³

2016

Phys. Rev. A

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“…In the following, we label a click in the first detector as 0, a click in the second detector as 1, and the case where either no detection or double detections are observed as ∅, so that each party effectively produces one of three possible outcomes. The statistics observed in this situation as a function of the polarization measurements and the detection efficiency (or equivalently the losses between the source and the detectors) are described in [21].…”

Section: Approximating Photonic Experimentsmentioning

confidence: 99%

Randomness in post-selected events

et al. 2016

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Bell inequality violations can be used to certify private randomness for use in cryptographic applications. In photonic Bell experiments, a large amount of the data that is generated comes from no-detection events and presumably contains little randomness. This raises the question as to whether randomness can be extracted only from the smaller post-selected subset corresponding to proper detection events, instead of from the entire set of data. This could in principle be feasible without opening an analogue of the detection loophole as long as the min-entropy of the post-selected data is evaluated by taking all the information into account, including no-detection events. The possibility of extracting randomness from a short string has a practical advantage, because it reduces the computational time of the extraction. Here, we investigate the above idea in a simple scenario, where the devices and the adversary behave according to i.i.d. strategies. We show that indeed almost all the randomness is present in the pair of outcomes for which at least one detection happened. We further show that in some cases applying a pre-processing on the data can capture features that an analysis based on global frequencies only misses, thus resulting in the certification of more randomness. We then briefly consider non-i.i.d strategies and provide an explicit example of such a strategy that is more powerful than any i.i.d. one even in the asymptotic limit of infinitely many measurement rounds, something that was not reported before in the context of Bell inequalities.

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“…The methods presented above are general and can be adjusted to any bipartite Bell experiment. We focus and describe in the following the architecture of optical implementations based on polarization measurements of entangled photons distributed from an SPDC source (see figure 1), which was thoroughly analysed in [21]. The source is characterized by three adjustable quantities: two squeezing parameters g 1 and g 2 and a total number of modes N onto which the photons may be distributed.…”

Section: Realistic Optical Implementationsmentioning

confidence: 99%

“…Each mode locally splits into two orthogonal polarizations. In terms of bosonic creation operators, the un-normalized state produced by S is given by [21]: All the different types of losses including detectors inefficiencies are modelled, without loss of generality, by two beam-splitters (not shown in figure 1) placed at any point between the users and the source. The transmittance η of these beam-splitters is the overall detection efficiency of the experiment.…”

Section: Realistic Optical Implementationsmentioning

confidence: 99%

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Optimal randomness generation from optical Bell experiments

et al. 2015

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Genuine randomness can be certified from Bell tests without any detailed assumptions on the working of the devices with which the test is implemented. An important class of experiments for implementing such tests is optical setups based on polarization measurements of entangled photons distributed from a spontaneous parametric down conversion source. Here we compute the maximal amount of randomness which can be certified in such setups under realistic conditions. We provide relevant yet unexpected numerical values for the physical parameters and achieve four times more randomness than previous methods.

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Challenging preconceptions about Bell tests with photon pairs

Cited by 24 publications

References 22 publications

Progress towards practical device-independent quantum key distribution with spontaneous parametric down-conversion sources, on-off photodetectors, and entanglement swapping

Progress towards practical device-independent quantum key distribution with spontaneous parametric down-conversion sources, on-off photodetectors, and entanglement swapping

Randomness in post-selected events

Optimal randomness generation from optical Bell experiments

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