Turning off quantum duality

Abstract

We provide the first experimental confirmation of a three-way quantum coherence identity possessed by single pure-state photons. Our experimental results demonstrate that traditional wave-particle duality is specifically limited by this identity. As a consequence, we show that quantum duality itself can be amplified, attenuated, or turned completely off. In the Young double-slit context this quantum coherence identity is found to be directly relevant, and it supplies a rare quantitative backup for one of Bohr's philosophical pronouncements.

Quantum duality: A source point of view

“…Such correspondences were first established quantitatively by Wootters and Zurek [3] and then followed by many others [4][5][6][7][8][9][10] to achieve a duality inequality, V 2 + D 2 1, between single quantum object wave interference visibility V and particle location distinguishability D. Extended studies have explored more specific physical properties, in addition to coherence and localized position, by establishing quantitative connections of the duality inequality with photon polarization [11][12][13][14][15][16], single-particle quantum states [17], and alternative coherence measures [18,19]. Recently, it has been demonstrated that the wave-particle property is connected to the self-entanglement between path and all remaining intrinsic properties (degrees of freedom) of the same single quantum object, leading to a threeway complementary identity [20,21], V 2 + D 2 + C 2 = 1, with C being the usual entanglement measure concurrence [22].…”

“…Almost all these previous quantitative studies [11][12][13][14][15][16][17][18][19][20][21] employ the scenario of single-particle double-slit interference, where in the analysis the two slits are often assumed to be ideal point sources of a single quantum particle. Unfortunately, no source properties such as the slit width, roughness, etc., have been taken into account in duality analyses.…”

Generalizing Wave-Particle Duality: Two-Qubit Extension of the Polarization Coherence Theorem

“…Equation 12and 5are the same, because for pure, bipartite states, it holds C 2 + P 2 = 1 [28][29][30][31]. According to [13], Equation 12is the correct single-particle duality restriction. This is so, because the restriction D 2 + V 2 ≤ 1 allows that both D and V simultaneously increase or decrease, it being possible that D = V = 0.…”

“…Let us now turn to another recent result in which wave-particle duality has been couched in quantum terms [13]. In this case, entanglement is addressed by writing (5) in the form [13,26]…”

“…Each of the two examples incorporates a feature hitherto neglected when dealing with wave-particle duality. In one case, the new feature is polarization [12] and in the other case it is entanglement [13]. We should stress that polarization can be defined whenever we deal with a two-state system and entanglement whenever we deal with two vector spaces, out of which we construct their tensor product space.…”