Quantum Information Processing, Vol. 5, No. 6, December 2006 (© 2006)
Cheating on Complementarity and Interference
by Translational – Internal Entanglement
Received December 6, 2005; accepted December 21, 2005; Published online July 28, 2006
We show that if internal and momentum states of an interfering particle are
entangled, then by measuring its internal state we may infer both path (corpuscu-
lar) and phase (wavelike) information with practically any precision, without the
complementarity constraints of which-path detection. This holds also for multi-
path–multistate conﬁgurations, allowing large amounts of information to be stored
in a single particle. We further show that highly complex particles (e.g., mole-
cules or macroscopic bodies) subject to ﬁelds that couple (entangle) their internal
and translational (momentum) states may undergo an irresversible randomization
(diffusion), manifest by the disappearance of the interference pattern, as if they
are subject to decoherence. Thus, translational-internal entanglement can give rise
to anomalies in quantum wavepacket propagation.
KEY WORDS: quantum interferometry; nonlocality; quantum information.
PAC S: 03.65.Ud; 03.65Vf; 03.75Dg.
The possibility of creating a single-particle quantum state where in transla-
tional (external) and internal degrees of freedom are inseparable, hereafter
referred to as translational-internal entanglement (TIE), is well established:
its best known manifestation is the Stern–Gerlach effect,
particle in a magnetic ﬁeld is deﬂected (its momentum is changed)
in accordance with its spin orientation. The obvious effect of TIE on a
near monoenergetic particle with many internal states travelling via many
Weizmann Institute of Science, 76100, Rehovot, Israel.
Department of Theoretical Physics, Palack
y University, 17. listopadu 50, 77200 Olomouc,
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