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| Title | Category | Date | Authors |
| Nonlinear phase shifts of light trapped in a two-component Bose-Einstein condensate University of Calgary | Publication | 2014-01-01 | C. Trail, K. Almutairi, D. Feder, B. C. Sanders | | Coupling of quantum fluctuations in a two-component condensateWe model frozen light stored via electromagnetically induced
transparency quantum-memory techniques in a Bose-Einstein
condensate. The joint evolution of the condensate and the frozen light is
typically modeled using coupled Gross-Pitaevskii equations for the two
atomic fields, but these equations are only valid in the mean-field limit.
Even when the mean-field limit holds individually for each atomic-field
component, coupling between the neglected fluctuations of the two
components could lead to a breakdown of the mean-field approximation
even if it is a good approximation for each species individually. We solve
and test the effect of coupled quantum fluctuations on coherent nonlinear
evolution of the frozen light pulse to see whether this two-species
condensate could enable nonlinear quantum optical phenomena.
Our analysis commences with a full second-quantized Hamiltonian
for a two-component condensate. The field operators are broken
up into a mean-field and a quantum fluctuation component. The
quantum fluctuations are truncated to lowest non-vanishing order.
The transformation diagonalizing the second-quantized approximate
Hamiltonian is described by coupled differential equations that are solved
with a power series expansion. We compare the consequent dynamics
with the mean-field evolution given by the two-component GrossPitaevskii equation. University of Calgary | Presentation | 2013-02-07 | C. Trail, B. C. Sanders | | Optical self-phase modulation via nonlinear spin-wave dynamics in a BECLight can be stored in Bose-Einstein condensates for more than one second using quantum memory techniques based on electromagnetically induced transparency [1]. In recent theoretical work [2], Rispe et al. proposed a method for storing photons in Bose-Einstein condensates to create a photon-photon gate. This gate uses the collisions between atoms in order to generate a phase shift that is dependent on the presence or absence of photons. We go beyond the single photon case considered in the previous scheme [2] to the many-photon case in the mean-field treatment and under the Thomas-Fermi approximation, where this scheme leads to strong phase self-modulation. That medium will allow superposition of an arbitrary number of photons to undergoing nonlinear evolution and in particular produce "cat states" [3]. We generate "cat states" [3] from coherent states through the collision-induced interaction.
References: [1] R. Zhang, S. R. Garner, and L.V. Hau, Phys. Rev. Lett. 103, 233602 (2009). [2] A. Rispe, B. He, and C. Simon ,Phys. Rev. Lett. 107, 043601 (2011). [3] B. Yurke, and D. Stoler, Phys. Rev. Lett. 57, 13 (1986). University of Calgary | Presentation | 2012-07-27 | K. Almutairi, C. Trail, C. Simon, B. C. Sanders | | Enhanced Spin Squeezing Through Quantum Control of QuditsSpin squeezed states have applications in metrology and quantum information processing. While there has been significant progress in producing spin squeezed states and understanding their properties, most spin squeezing research to date has focused on ensembles of qubit spins. We explore squeezed state production in an ensemble of spin f>1/2 alkali atoms (qudits). Collective interactions are achieved through coherent quantum feedback of a laser probe, interacting with the ensemble through the Faraday interaction. This process can be enhanced through further control of the atomic qudits. We control the internal atomic state both before and after the collective interaction. Initial preparation increases the collective squeezing parameter through enhancement of resolvable quantum fluctuations. Qudit control can then be used to map entanglement created by the collective interaction to different pseudo-spin subspaces where they are metrologically useful, e.g., the clock transition or the stretched state for magnetometry. In the latter case, additional internal control can be used to squeeze the individual atoms, further enhancing the total squeezing in a multiplicative manner. The actual squeezing will depend on a balance between the enhanced coupling and decoherence. These considerations highlight the unique capabilities of our platform: we are able to transfer coherences and correlations between subspaces and integrate control tools to explore a wider variety of nonclassical states, with ultimate application in sensors or other quantum information processors. University of Calgary | Presentation | 2012-06-14 | N. L. Norris, C. Trail, S. P. Jessen, H. I. Deutsch | | Enhanced spin squeezing through quantum control of quditsSpin squeezed states have applications in metrology and quantum information processing. While there has been significant progress in producing spin squeezed states and understanding their properties, most spin squeezing research to date has focused on ensembles of qubit spins. We explore squeezed state production in an ensemble of spin f>1/2 alkali atoms (qudits). Collective interactions are achieved through coherent quantum feedback of a laser probe, interacting with the ensemble through the Faraday interaction. This process can be enhanced through further control of the atomic qudits. We control the internal atomic state both before and after the collective interaction. Initial preparation increases the collective squeezing parameter through enhancement of resolvable quantum fluctuations. Qudit control can then be used to map entanglement created by the collective interaction to different pseudo-spin subspaces where they are metrologically useful, e.g., the clock transition
or the stretched state for magnetometry. In the latter case, additional internal control can be used to squeeze the individual atoms, further enhancing the total squeezing in a multiplicative manner. The actual squeezing will depend on a balance between the enhanced coupling and decoherence. These considerations highlight the unique capabilities of our platform: we are able to transfer coherences and correlations between subspaces and integrate control tools to explore a wider variety of nonclassical states, with ultimate application in sensors or other quantum information processors. University of Calgary | Presentation | 2012-07-27 | N. L. Norris, C. Trail, S. P. Jessen, H. I. Deutsch |
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