Scientific background
Although the postulates of quantum mechanics were laid down nearly a century ago, quantum measurement and the experimental understanding of macroscopic quantum coherence (or lack thereof) remain elusive [1-3] The simplistic, projective Copenhagen interpretation [4] of quantum measurement becomes increasingly unsatisfactory as experimental interest shifts from small and well-isolated atomic and sub-atomic particles to larger mesoscopic, interacting quantum systems. Control over individual quanta and their interactions to build up larger and more complex systems is thus an exciting new frontier for experimental physics and computer science [5]. A broad effort within experimental physics is now aimed at studying this quantum-classical interface and pushing the limits of decoherence to make larger quantum systems.
Quantum optics with atomic ensembles [6-8] is a remarkable combination of two extremes. On the one hand they are composed of individual atomic systems that each posses narrow homogeneous linewidths. On the other hand, the optical information is registered in the combined many-body system, in which individual components are colliding, dephasing, and generally interacting with a complex internal and external environment.
Despite this, storage of optical information in an atomic ensemble and its subsequent retrieval have been demonstrated using dynamically modulated Electromagnetically Induced Transparency (EIT) [9-10] on three level atoms and Controlled Reversible Inhomogeneous Broadening (CRIB) [11-12] on two level systems. Several other exciting schemes are being actively studied worldwide.
In the limit of low power we expect the susceptibility of the EIT medium to be given by [7]
Where n is the atomic density, mge is the dipole matrix element, e0 is the permittivity of the vacuum, gij is the relaxation rate between the state i to state j, W is the Rabi frequency of the pump and w is the detuning from the bare probe resonance. This expression is very illuminating, since it gives us the connection between the transmission coefficient and refractive index of the material. Its dispersive character leads to a very narrow (assuming the relaxation rates are slow) transparency window and a very slow group velocity for the propagating probe. If the pump power is adiabatically ramped down while the probe is propagating in the vapor, the light will be adiabatically transferred into an atomic coherence and the group velocity goes to zero (stored light).
Experimentally, the dramatic demonstration of the slowing and storing of light in atomic vapors at room temperatures using EIT, has drawn work towards this implementation. Many groups worldwide (including our own) are actively developing this technology, typically using heated Rubidium vapor placed in a magnetically shielded and controlled environment.
Interesting applications using Rubidium vapor include storage of optical images [13], four wave mixing [14], interferometer delay lines [15] and single photon storage [16].
In recent years, ensembles of trivalent rare-earth ions (doping a crystal matrix) have been coming to the fore [17]. These include Thulium, Erbium, Europium, Neodymium or Praseodymium ions. Typically they are doped into Y2SiO5 or LiNbO3 crystals. When these doped crystals containing the rare earth ions are cooled to liquid Helium temperatures, the optical excitation of the ions is remarkably shielded from the noise in the solid state crystal matrix. The lifetime of optically excited states can be as long as a few seconds and the homogenous linewidths are remarkably narrow (as narrow as a few kHz) [18]. The inhomogeneous linewidths are significantly broader (a few GHz wide, typically). However, recent experimental protocols such as CRIB can overcome this limitation. Storage and retrieval of optical pulses with efficiencies of tens of percents are now the state of the art [17].
Research Objectives
- Storage and retrieval of complex topologically stable (spatially) EIT states in atomic vapors, and measurement of their complex diffusion.
- Storage and retrieval of spatially and temporally shaped pulses in a Tm+3 doped crystal and characterization of relaxation and coherence times.
- Storage and retrieval of few photon pulses and their dynamical manipulation while stored to retrieve in new modes. Characterization of the resulting pulses by quantum-optical state tomography. This may allow us to demonstrate squeezing and entanglement of the photons.
W. H. Zurek, Rev. Mod. Phys. 75, 715 (2003).
A. J. Leggett, Science 307, 871 (2005).
M. Schlosshauer, Rev. Mod. Phys. 76, 1267 (2004).
N. Bohr, The quantum postulate and the recent development of atomic theory, Nature (London) 121, 580 (1928); N. Bohr, in Albert Einstein: Philosopher-Scientist, edited by P. A. Schilpp (Open Court, Evanston), p. 200 (1949).
M. A. Nielsen, I. L. Chuang, Quantum Computation and Quantum Information (Cambridge Univ. Press, Cambridge, 2000).
L.-M. Duan, J. I. Cirac, P. Zoller, and E. S. Polzik, Phys. Rev. A 85, 5643 (2000).
M. Fleischhauer and M. D. Lukin, Phys. Rev. A 65, 022314 (2002); M. Fleischhauer, A. Imamoglu, and J. P. Marangos, Rev. Mod. Phys. 77, 633 (2005).
S. A. Moiseev and S. Kröll, Phys. Rev. Lett. 87, 173601 (2001).
C. Liu et al., Nature (London) 409, 490 (2001).
D. Phillips et al., Phys. Rev. Lett. 86, 783 (2001).
B. Kraus et al., Phys. Rev. A 73, 020302R (2006).
M. U. Staudt et al., Phys. Rev. Lett. 98, 113601 (2007).
M. Shuker et al. Phys. Rev. Lett. 100, 223601 (2008).
M. Jain et al., Phys. Rev. Lett. 77, 4326 (1996).
Zhimin Shi et al., Phys. Rev. Lett. 99, 240801 (2007).
T. B. Pittman and J. D. Franson, Phys. Rev. A 66, 062302 (2002).
W. Tittel et al., Laser & Photon. Rev., 1–24 (2009).
D. L. Mc Auslan, J. J. Longdell, and M. J. Sellars, accepted to Phys. Rev. A (2009). arXiv:0908.1994
R. Pugatch et. al, Phys. Rev. Lett. 98, 203601 (2007)
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