High-visibility interference in a Bell-inequality experiment for energy and time

Kwiat, Paul G.; Steinberg, Aephraim M.; Chiao, Raymond Y.

doi:10.1103/physreva.47.r2472

Cited by 327 publications

(310 citation statements)

References 23 publications

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“…It is currently realized that the violation of Bell's inequalities [27,29,31,34] should be attributed to the non-commutative nature of the distribution D rather than to non-locality; quantum mechanics does not involve ordinary probabilities nor ordinary correlations. The violation of the classical inequality, observed experimentally [144,145,146,147,148,149] arises when one puts together outcomes of measurements performed in different experimental contexts, and this may itself be a problem [150,151,152,153,154]. The discussion of § 8.3.4 shows how quantum and ordinary correlations may be reconciled in the context of a thought experiment where one attempts to measure simultaneously, with a unique setting, all spin components.…”

Section: Measurements In Underlying Classical Theorymentioning

confidence: 99%

Understanding quantum measurement from the solution of dynamical models

Allahverdyan¹,

Balian²,

2013

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The quantum measurement problem, to wit, understanding why a unique outcome is obtained in each individual experiment, is currently tackled by solving models. After an introduction we review the many dynamical models proposed over the years for elucidating quantum measurements. The approaches range from standard quantum theory, relying for instance on quantum statistical mechanics or on decoherence, to quantum-classical methods, to consistent histories and to modifications of the theory. Next, a flexible and rather realistic quantum model is introduced, describing the measurement of the z-component of a spin through interaction with a magnetic memory simulated by a Curie-Weiss magnet, including N 1 spins weakly coupled to a phonon bath. Initially prepared in a metastable paramagnetic state, it may transit to its up or down ferromagnetic state, triggered by its coupling with the tested spin, so that its magnetization acts as a pointer. A detailed solution of the dynamical equations is worked out, exhibiting several time scales. Conditions on the parameters of the model are found, which ensure that the process satisfies all the features of ideal measurements. Various imperfections of the measurement are discussed, as well as attempts of incompatible measurements. The first steps consist in the solution of the Hamiltonian dynamics for the spin-apparatus density matrixD(t). Its off-diagonal blocks in a basis selected by the spin-pointer coupling, rapidly decay owing to the many degrees of freedom of the pointer. Recurrences are ruled out either by some randomness of that coupling, or by the interaction with the bath. On a longer time scale, the trend towards equilibrium of the magnet produces a final stateD(t f ) that involves correlations between the system and the indications of the pointer, thus ensuring registration. AlthoughD(t f ) has the form expected for ideal measurements, it only describes a large set of runs. Individual runs are approached by analyzing the final states associated with all possible subensembles of runs, within a specified version of the statistical interpretation. There the difficulty lies in a quantum ambiguity: There exist many incompatible decompositions of the density matrixD(t f ) into a sum of sub-matrices, so that one cannot infer from its sole determination the states that would describe small subsets of runs. This difficulty is overcome by dynamics due to suitable interactions within the apparatus, which produce a special combination of relaxation and decoherence associated with the broken invariance of the pointer. Any subset of runs thus reaches over a brief delay a stable state which satisfies the same hierarchic property as in classical probability theory; the reduction of the state for each individual run follows. Standard quantum statistical mechanics alone appears sufficient to explain the occurrence of a unique answer in each run and the emergence of classicality in a measurement process. Finally, pedagogical exercises are proposed and lessons for future works on m...

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Section: Measurements In Underlying Classical Theorymentioning

confidence: 99%

Understanding quantum measurement from the solution of dynamical models

Allahverdyan¹,

Balian²,

2013

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“…It is important to note that the increase of visibility described above could also be observed with optical fields exhibiting classical correlations [17,18]. To exclude this possibility we also test time correlations of the photon pairs generated by our source [14,20]. This is shown and discussed in section V. Section VI concludes the paper.…”

Section: Introductionmentioning

confidence: 81%

“…If the MZ interferometer's detuning is equal to n roundtrips in the FP resonator which is placed in the signal-photon path, one can not distinguish between two possible events: a) either the idler photon takes the shorter arm of the MZ and the signal photon makes m roundtrips in the FP, where m is an integer; b) or the idler photon takes the longer arm of the MZ and the signal photon makes m + n roundtrips. This option of two indistinguishable paths restores the interference [11,12,13,14]. The longer detuning ∆t, the more unbalanced interfering probability amplitudes (corresponding to cases a) and b)) and consequently the lower visibility.…”

Section: A Setup With a Gaussian Filtermentioning

confidence: 97%

“…First high-visibility interference experiments of this type were performed using Michelson interferometer [12], reaching a visibility of 87%. Later experiments utilized spatially separated Mach-Zehnder interferometers to measure nonlocal interference [13,14]. Interference was observed also in mixing of signal photons produced by SPDC in two nonlinear crystals [15].…”

Section: Introductionmentioning

confidence: 99%

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Experimental verification of energy correlations in entangled photon pairs

et al. 2003

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Properties of entangled photon pairs generated in spontaneous parametric down-conversion are investigated in interference experiments. Strong energy correlations are demonstrated in a direct way. If a signal photon is detected behind a narrow spectral filter, then interference appears in the Mach-Zehnder interferometer placed in the route of the idler photon, even if the path difference in the interferometer exceeds the coherence length of the light. Narrow time correlations of the detection instants are demonstrated for the same photon-pair source using the Hong-Ou-Mandel interferometer. Both these two effects may be exhibited only by an entangled state.

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“…Here also the demonstrations by Moerner and Orrit of absorption and fluorescence of single molecules trapped in a solid matrix should be mentioned as they led to the also important discovery of antibunching of emitted photons (Basché et al 1992). Franson (1989) and Kwiat et al (1993) have in two-photon interference experiments shown sinusoidal fringes with 80% visibility, such as predicted by QM, violating Bell inequality by 16 standard deviations. More recently Salart et al (2008) and Yin et al (2013), following a proposal by Eberhart (1989) for a 12-h continuous space-like Bell inequality exploiting the Earth's self-rotation, discuss the possibility of superluminal interference at ca 20 km distance.…”

Section: The 'Interaction Hypothesis'mentioning

confidence: 94%

Quantum entanglement: facts and fiction – how wrong was Einstein after all?

Nordén

2016

Quart. Rev. Biophys.

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Abstract. Einstein was wrong with his 1927 Solvay Conference claim that quantum mechanics is incomplete and incapable of describing diffraction of single particles. However, the Einstein-Podolsky-Rosen paradox of entangled pairs of particles remains lurking with its 'spooky action at a distance'. In molecules quantum entanglement can be viewed as basis of both chemical bonding and excitonic states. The latter are important in many biophysical contexts and involve coupling between subsystems in which virtual excitations lead to eigenstates of the total Hamiltonian, but not for the separate subsystems. The author questions whether atomic or photonic systems may be probed to prove that particles or photons may stay entangled over large distances and display the immediate communication with each other that so concerned Einstein. A dissociating hydrogen molecule is taken as a model of a zero-spin entangled system whose angular momenta are in principle possible to probe for this purpose. In practice, however, spins randomize as a result of interactions with surrounding fields and matter. Similarly, no experiment seems yet to provide unambiguous evidence of remaining entanglement between single photons at large separations in absence of mutual interaction, or about immediate (superluminal) communication. This forces us to reflect again on what Einstein really had in mind with the paradox, viz. a probabilistic interpretation of a wave function for an ensemble of identically prepared states, rather than as a statement about single particles. Such a prepared state of many particles would lack properties of quantum entanglement that make it so special, including the uncertainty upon which safe quantum communication is assumed to rest. An example is Zewail's experiment showing visible resonance in the dissociation of a coherently vibrating ensemble of NaI molecules apparently violating the uncertainty principle. Einstein was wrong about diffracting single photons where space-like anti-bunching observations have proven recently their non-local character and how observation in one point can remotely affect the outcome in other points. By contrast, long range photon entanglement with immediate, superluminal response is still an elusive, possibly partly misunderstood issue. The author proposes that photons may entangle over large distances only if some interaction exists via fields that cannot propagate faster than the speed of light. An experiment to settle this 'interaction hypothesis' is suggested.In 1935, Einstein, Podolsky and Rosen (EPR) presented a paradox, which seemed to imply a fundamental discrepancy between quantum and classical mechanics and which they meant proves that the former is not a 'complete theory' . Einstein (1936) elaborated on the theme with a more nuanced description later, in what sense he considers quantum mechanics (QM) incomplete. His concern that it is the way QM is applied to singular particulate systems rather than whether it is a correct theory, was my inspiration for revisiting these grounds a...

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High-visibility interference in a Bell-inequality experiment for energy and time

Cited by 327 publications

References 23 publications

Understanding quantum measurement from the solution of dynamical models

Understanding quantum measurement from the solution of dynamical models

Experimental verification of energy correlations in entangled photon pairs

Quantum entanglement: facts and fiction – how wrong was Einstein after all?

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