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International Conference on Quantum Information

Decoherence and Distinguishability in Optical and Atomic Experiments on Quantum Tomography

Aephraim M. Steinberg

Published Jan 1, 2007• 0 citations
Publisher

Abstract

I describe recent work in our group on tomography and coherence control in real-world systems, specifically, multi-photon entangled states and ultracold atoms in optical lattices. Near but imperfect indistinguishability complicates tomography in the former case, while inhomogeneous broadening presents challenges in the latter. I present the current status of our work to overcome both problems, and results on tomography of 3-photon states along with pulse-echo studies of decoherence in optical lattices.

DOI
10.1364/icqi.2007.iwb3

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I describe recent work in our group on tomography and coherence control in real-world systems, specifically, multi-photon entangled states and ultracold atoms in optical lattices. Near but imperfect indistinguishability complicates tomography in the former case, while inhomogeneous broadening presents challenges in the latter. I present the current status of our work to overcome both problems, and results on tomography of 3-photon states along with pulse-echo studies of decoherence in optical lattices.
Recent developments in quantum gas microscopy open up the possibility of real-time observation of quantum many-body systems. To understand the dynamics of atoms under such circumstances, we formulate the dynamics under a real-time spatially resolved measurement and show that, in an appropriate limit of weak spatial resolution and strong atom-light coupling, the measurement indistinguishability of particles results in complete suppression of relative positional decoherence. As a consequence, quantum correlation in the multiparticle dynamics persists under a minimally destructive observation. We numerically demonstrate this for ultracold atoms in an optical lattice. Our theoretical framework can be applied to the feedback control of quantum many-body systems which may be realized in subwavelength-spacing lattice systems.
We formulate the dynamics of quantum many-body systems under real-time spatially-resolved measurement, and show that, in the continuous measurement limit, the indistinguishability of identical particles results in the complete suppression of relative positional decoherence. As a consequence, the indistinguishability persists in the course of quantum dynamics under weak continuous observation. We numerically demonstrate this result for ultracold atoms in an optical lattice. Our results can be applied to quantum feedback control of quantum many-body systems which may be realized in subwavelength spacing lattice systems.
A recently proposed, photon echo related approach to quantum state storage in atomic ensembles employs controlled reversible inhomogeneous broadening (CRIB). Beyond storage, a modified version of CRIB promises controlled quantum state manipulations. As the implementation of CRIB is currently still challenging, we investigate state transformation based on stimulated photon echoes. Specifically, we show how to translate an all optical, beamsplitter based setup into a photon echo based setup, and we simulate a photon echo based POVM (positive operator valued measure) measurement using Maxwell-Bloch equations.
Using on-demand coherence conversion via optical locking, a dynamic coherent control of the collective atom phase has been demonstrated for longer photon storage beyond the critical constraint of spin phase decay time, where the storage time can be extended up to hours in a rare-earth-doped solid. Coherent transient phenomena such as photon echoes have been investigated for frozen phase decay via coherent population transfer using a simple deshelving optical pulse pair. Unlike the rephasing halt applied to two-pulse photon echoes, where optical decoherence is accelerated by spin inhomogeneous broadening, a completely atom phase-locked coherence conversion has been observed in three-pulse photon echoes, resulting in spin dephasing-free coherence control. Here, the mechanism of the atom phase-locked coherence conversion via optical locking has been investigated in a solid medium whose optical transition is imperfect, where partial coherence is lost via optical depth-dependent imperfect population transfer. The relationship between coherence loss and optical depth is analyzed, where nearly perfect photon echo efficiency can be obtained for ultralong photon storage in an optically thick medium.
Ultracold atoms in optical lattices have proven to provide an extremely clean and controlled setting to explore quantum many-body phases of matter. Now, imaging of atoms in such lattice structures has reached the level of single-atom sensitive detection combined with the highest resolution down to the level of individual lattice sites. This has opened up fundamentally new opportunities for the characterization and the control of quantum many-body systems. Here we give a brief overview of this field and explore the opportunities offered for future research.