1,721,348 research outputs found
Efficient optomechanical cooling in one-dimensional interferometers
No full textWe present a scattering model which enables us to describe the mechanical force, including the velocity dependent component, exerted by light on polarizable massive objects in a general one-dimensional optical system. We show that the light field in an interferometer can be very sensitive to the velocity of a moving scatterer. We construct a new efficient cooling scheme, ‘external cavity cooling’, in which the scatterer, that can be an atom or a moving micromirror, is spatially separated from the cavity
Quantum cryptography with squeezed light and post-selection
No full textThe role of squeezing and post-selection in continuous variable quantum key distribution is investigated. The scheme is based on the transmission of weak, amplitude-squeezed pulses of light in four discrete quantum states. It is shown that squeezing creates strong correlations between the signals of the legitimate receiver and a potential eavesdropper. Post-selection of the received pulses can therefore be used to reduce the eavesdropper's knowledge of the raw key. This increases the secret bit rate by orders of magnitude over large distances even for modest amounts of squeezing. (This is similar to paper number eP13935 which is available below.
Semiclassical Monte-Carlo simulations: multiple interacting particles and optical modes
No full textSemiclassical models of atom-light interaction have been an important tool in the simulation of cold matter since the beginnings of laser cooling. While they cannot be applied to ultracold systems, e.g., for ground state cooling and quantum statistics, there are still many applications in the micro- to milli-Kelvin regime where semiclassical simulations have an important role to play today, in particular where many particles and many optical modes are involved. I will review semiclassical multiparticle and multimode Monte-Carlo methods and discuss their application to several specific systems, from cavity and mirror-mediated cooling to ion Coulomb crystals
Quantum theory of mirror-mediated atom cooling
No full textWe have recently suggested that a polarisable particle may be cooled by its interaction with a monochromatic laser beam if the transmitted beam is reflected back onto the particle by a mirror. The interference of the incoming beam with the reflected beam, which carries a phase imprinted by the particle at an earlier time, leads to a non-conservative potential and to frictional cooling. This simple scheme poses some challenging problems for accurate modelling. On one hand, cooling relies on the back-action of the particle-light interaction on the light itself and therefore the electromagnetic field must be treated dynamically, in contrast to standard free-space laser cooling methods. On the other hand, the system is intrinsically non-Markovian and thus cannot be described by the interaction of the particle with a single or a few discrete quantised modes coupled to a thermal reservoir, as in the case of cavity-mediated cooling [1]. Instead, a mathematical description must either keep track of the system at earlier times or, equivalently by Fourier transform, contain a continuous set of quantised modes [2]. In this talk, I will present a quantum mechanical model following this latter approach. Friction and momentum diffusion can be derived analytically to lowest order in the atom-light coupling strength. This allows us to predict cooling times and steady-state temperatures as a function of system parameters. Finally, we use corresponding semiclassical Monte-Carlo simulations [3] to corroborate these results and to access certain parameter regimes outside the validity of the analytical model
The role of squeezing in quantum key distribution based on homodyne detection and post-selection
No full textThe role of squeezing in quantum key distribution with continuous variables based on homodyne detection and post-selection is investigated for several specific eavesdropping attacks. It is shown that amplitude squeezing creates strong correlations between the signals of the legitimate receiver and a potential eavesdropper. Post-selection of the received pulses can therefore be used to reduce the eavesdropper's knowledge of the raw key, which increases the secret key rate by orders of magnitude over large distances even for modest amounts of squeezing
Effect of all-optical phase regeneration on fiber transmission capacity
No full textWe investigate theoretically the benefits of using all-optical phase regeneration in a long-haul fiber optic link. We simulate numerically the bit-error rate of a WDM optical communication system over many fiber spans with periodic re-amplification and compare the results obtained with and without the use of a phase regenerator at half the transmission distance. Our results suggest that, depending on the modulation format, a significantly improved performance by up to 1.5 orders of magnitude can be achieved
Effects of pulse self-focusing on supercontinuum generation in multimode optical fibers
No full textWe investigate the nonlinear propagation of ultra-short pulses in multimode optical fibers. At high peak powers, close to the critical power for self-focusing in bulk materials, a four-wave mixing process is observed which transfers power from the fundamental fiber mode to higher-order modes and leads to transverse spatial pulse compression. The interplay of this spatial effect with the temporal dynamics responsible for supercontinuum generation is discussed
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