Abstract

I discuss the delayed choice quantum eraser experiment by drawing an analogy to a Bell-type measurement and giving a straightforward account in standard quantum mechanics. The delayed choice quantum eraser experiment turns out to resemble a Bell-type scenario in which the resolution of the paradox is rather trivial, and so there really is no mystery. At first glance, the experiment suggests that measurements on one part of an entangled photon pair (the idler) can be employed to control whether the measurement outcome of the other part of the photon pair (the signal) produces interference fringes at a screen after being sent through a double slit. Significantly, the choice whether there is interference or not can be made long after the signal photon encounters the screen. The results of the experiment have been alleged to invoke some sort of backwards in time influence. I argue that this issue can be eliminated by taking into proper account the role of the signal photon. Likewise, in the de Broglie–Bohm picture the trajectories of the particle can be given a well-defined description at any instant of time during the experiment. Thus, it is again clear that there is no need to resort to any kind of backwards in time influence.Quanta 2019; 8: 44-56.

Highlights

  • No phenomenon is a phenomenon until it is an idler) can be employed to control whether the meaobserved phenomenon. [1, p. 14]

  • I shall discuss a modified trajectories of the particle can be given a well-defined version of Wheeler’s delayed choice experiment, which description at any instant of time during the experi- was first proposed by Scully and Druhl in [14] and later ment

  • For the other, assuming the signal photon to be in one In the old days of quantum mechanics it was believed of the basis states before it or the idler photon were mea- that the loss of interference in double slit experiments sured puts one into the business of hidden variable theo- were due to Heisenberg’s uncertainty principle, for no ries

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Summary

Johannes Fankhauser

Idiscuss the delayed choice quantum eraser exper- 1 Introduction iment by drawing an analogy to a Bell-type measurement and giving a straightforward account in Delayed choice scenarios in slit experiments as found standard quantum mechanics. Alice’s is similar: When Alice obtains 0, Bob is going (1) to see 0 as well in the D3,4 measurement (the same holds for outcome 1) In this case, just as previously, The states of the photons are taken to be qubit states. In the case of the meatum eraser later, call Alice’s photon the signal photon and surement at detector D1,2, i.e. in the diagonal basis, Bob. Bob’s photon the idler. Ror M to measure the idler photon in the computational we see that the conditional statistics are the basis {|0 , |1 } or the mirror is removed and the photon same as in the previous scenario; that is, the statistics are travels to detector D1,2 where Bob performs a measure- the same as those which would be recorded if Bob’s meament in the diagonal basis {|+ , |− }, where surement had come first rather than Alice’s: conditioned. + |1 ) , on Bob recording a +(–) result, Alice’s will record 50% outcome 0 and 50% outcome 1

It is important to note that on an operational view in
BS BS y
By integrating out the idler degrees of freedom we find
Findings
Bell inequalities can equally well be confirmed via post
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