Wave-particle dualism and complementarity unraveled by a different mode

Abstract

The precise knowledge of one of two complementary experimental outcomes prevents us from obtaining complete information about the other one. This formulation of Niels Bohr's principle of complementarity when applied to the paradigm of wave-particle dualism-that is, to Young's double-slit experiment-implies that the information about the slit through which a quantum particle has passed erases interference. In the present paper we report a double-slit experiment using two photons created by spontaneous parametric down-conversion where we observe interference in the signal photon despite the fact that we have located it in one of the slits due to its entanglement with the idler photon. This surprising aspect of complementarity comes to light by our special choice of the TEM 01 pump mode. According to quantum field theory the signal photon is then in a coherent superposition of two distinct wave vectors giving rise to interference fringes analogous to two mechanical slits.T he double-slit experiment has served as a source of inspiration for more than two centuries. Indeed, Thomas Young (1) has used it to argue in favor of the wave theory of light rather than the corpuscular one of Isaac Newton (2). In the early days of quantum mechanics it was central to the dialogue (3) between Albert Einstein and Bohr on epistemological problems in atomic physics. Moreover, it was the starting point of the path integral formulation (4) of quantum mechanics by Richard Feynman.Today the question of "which-slit" versus "interference" in the double-slit configuration (5) is as fascinating and relevant (6) as it was in the early days of quantum mechanics. In particular, the understanding of the physical origin (7) of the disappearance of the fringes in the presence of which-slit information has come a long way. Werner Heisenberg in the context of the uncertainty relation (8), Bohr in his discussion with Einstein (3) on the recoiling slit, and others (9) have argued in favor of an uncontrollable momentum transfer (7). However, the Gedanken experiments of the quantum eraser (10) and the micromaser "welcher Weg" detector (11) have identified entanglement and the availability of information as the main culprit. Indeed, the seminal atom interferometer experiment (12) as well as the realization (13) of the quantum eraser have made a clear decision against momentum transfer in favor of entanglement. As a result, today the principle of complementarity (14) is widely accepted (15) in the form (16): "If information on one complementary variable is in principle available even if we choose not to 'know' it… we will lose the possibility of knowing the precise value of the other complementary variable."In the present paper we report the results of a double-slit experiment that brings out an additional layer of this principle. We employ the entanglement between the signal and the idler photon created in spontaneous parametric down-conversion (SPDC) (17) to obtain by a coincidence measurement of the two photons which-slit information about the signal ...

Challenges to Bohr’s Wave-Particle Complementarity Principle

“…There is equivocation in two places (p. 9314 and p. 9316) about the use of mechanical slits in Menzel et al [10]. On p. 9314, their abstract creates an ambiguity as to whether mechanical slits were actually used when they say, "According to quantum field theory the signal photon is then in a coherent superposition of two distinct wave vectors giving rise to interference fringes analogous to two mechanical slits."…”

“…In 2012 Menzel et al [10] reported that they had successfully conducted a Young's two slit experiment in which they had located which slit a photon passed through, and contrary to Bohr's complementarity principle still obtained an interference pattern.…”

“…On p. 9314, their abstract creates an ambiguity as to whether mechanical slits were actually used when they say, "According to quantum field theory the signal photon is then in a coherent superposition of two distinct wave vectors giving rise to interference fringes analogous to two mechanical slits." [10] The text of their paper describes the presence of two mechanical slits, Here are two such cases without mechanical slits that gave rise to interference fringes.…”

“…Both determined the traversed slit taken by the interference particle by observing the entangled particle. The interference particle was designated the "signal" particle and the observed particle was designated the "idler" particle by [10]. Whereas [9] called the observed particle, the "partner" particle.…”

“…Both references [9] and [10] utilized a source emitting entangled particle pairs. Both determined the traversed slit taken by the interference particle by observing the entangled particle.…”