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Physical Review A

Interferometric technique for engineering indistinguishability and entanglement of photon pairs

David A. Branning, Warren P. Grice, Reinhard K. Erdmann, Ian A. Walmsley

Published Jun 15, 2000• 30 citations
Publisher

Abstract

We give a detailed account of a recently introduced technique to suppress distinguishing information in the space-time component of the state vector of a pair of photons. The method works by creating interference between two possible ways for each photon to occupy any given space-time mode. Under certain conditions, this technique also allows the preparation of the two photons in a highly entangled space-time state.

DOI
10.1103/physreva.62.013814

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We give a detailed account of a recently introduced technique to suppress distinguishing information in the space-time component of the state vector of a pair of photons. The method works by creating interference between two possible ways for each photon to occupy any given space-time mode. Under certain conditions, this technique also allows the preparation of the two photons in a highly entangled space-time state.
We present a novel interferometric technique for suppressing distinguishing information in the space-time component of the state vector of an entangled pair of photons by providing two indistinguishable ways for each photon to occupy any given space-time mode. We demonstrate this method by using spontaneous parametric down-conversion to generate a pair of photons in the state with the least distinguishing information consistent with the set of modes available. The technique also allows the preparation of the two photons in a highly entangled space-time state provided certain criteria are met.
One of the central principles of quantum mechanics is that if there are multiple paths that lead to the same event and there is no way to distinguish between them, interference occurs. It is often assumed that distinguishing information in the preparation, evolution, or measurement of a system is sufficient to destroy interference. However, it is still possible for photons in distinguishable, separable states to interfere due to the indistinguishability of paths corresponding to possible exchange processes. Here we experimentally measure an interference signal that depends only on the multiparticle interference of four photons in a four-port interferometer despite pairs of them occupying distinguishable states.
We review recent theoretical and experimental works where are proposed and demonstrated how to use photon pairs created by spontaneous parametric down-conversion to generate entangled states of D-dimensional quantum systems, or qudits. This is the first demonstration of high-dimensional entanglement based on the intrinsic transverse momentum entanglement of the type-II down-converted photons. The qudit space is defined by an aperture made up of an opaque screen with D slits (paths), placed in the arms of the twin photons. By manipulating the pump beam profile we can prepare different entangled states of these possible paths. We focus our attention on an important case for applications in quantum information: the maximally entangled states. Experimental results for qudits with D=4 and D=8 are shown and measuring a two-photon conditional interference, we also demonstrate the nonclassical character of the correlations.
When a single emitter is excited by two phase-coherent pulses with a time delay, each of the pulses can lead to the emission of a photon pair, thus creating a "time-bin-entangled" state. Double pair emission can be avoided by initially preparing the emitter in a metastable state. We show how photons from separate emissions can be made indistinguishable, permitting their use for multiphoton interference. Possible realizations are discussed. The method might also allow the direct creation of n-photon entangled states (n > 2).