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Quantum States and Number-Phase Uncertainty Relations Measured by Optical Homodyne Tomography

100%

Raymer M. G., Smithey D. T., Beck M., Cooper J.

Acta Physica Polonica A

1994

vol. 86

issue 1

71-80

Experiments have been performed to determine the Wigner distribution and the density matrix (and for pure states the wave function) of a light mode, by using tomographic inversion of a set of measured probability distributions for quadrature amplitudes. From these measurements the quantum distributions of optical phase and photon number have been obtained. The measurements of quadrature-amplitude distributions for a temporal mode of the electromagnetic field are carried out using balanced homodyne detection. We refer to this new method as optical homodyne tomography. Given the measured density matrix, one can experimentally infer any of the various quantum distributions of optical phase, in particular the Pegg-Barnett (or, equivalently, Shapiro-Shepard) phase distribution, the marginal Wigner distribution, and the Vogel-Schleich operational phase distribution. We have used this approach to make measurements of the number-phase uncertainty relation for coherent-state fields. The coherent states do not attain the minimum value for the number-phase uncertainty product, as set by the expectation value of the commutator of the number and phase operators; this is true theoretically and experimentally.

Quantum Optics of a Bose-Einstein Condensate

100%

Lewenstein M., You L., Cooper J.

Acta Physica Polonica A

1994

vol. 86

issue 1

173-190

We present a review of recent experimental and theoretical attempts to realize and investigate Bose-Einstein condensation in systems of cooled alkali atoms. We discuss a second quantized theory that describes quantum optics of such systems. We study in detail: (a) the weak field scattering off the condensate; and (b), the probing of the condensate with short laser pulses.

Stochastic Carrier Dynamics in Semiconductor Superlattices

52%

Fromhold T., Bujkiewicz S., Patanè A., Stapleton S., Sherwood D., Fowler D., Cooper J., Eaves L., Belyaev A., Krokhin A., Neumann A., Wilkinson P., Sankeshwar N., Henini M., Sheard F.

Acta Physica Polonica A

2006

vol. 109

issue 1

43-52

We explore a new regime of hot carrier dynamics, in which electrons in a superlattice miniband exhibit a unique type of stochastic motion when a magnetic field is tilted at an angleθ to the superlattice axis. Remarkably, the dynamics of a miniband electron in a tilted magnetic field reduce to a one-dimensional simple harmonic oscillator, of angular frequencyω_C cosθ, whereω_C is the cyclotron frequency, driven by a time-dependent plane wave whose angular frequency equals the Bloch frequencyω_B. At bias voltages for whichω_B=nω_C cosθ, where n is an integer, the electron orbits change from localised Bloch-like trajectories to unbounded stochastic orbits, which diffuse rapidly through intricate web patterns in phase space. To quantify how these webs affect electron transport, we make drift-diffusion calculations of the current-voltage curves including the effects of space-charge build up. When the magnetic field is tilted, our simulations reveal a large resonant peak, which originates from stochastic delocalisation of the electron orbits. We show that the corresponding quantised eigenstates change discontinuously from a highly localised character when the system is off resonance to a fully delocalised form when the resonance condition is satisfied.

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3 Acta Physica Polonica A

1 2006

2 1994

3 Cooper J.

1 Beck M.

1 Belyaev A.

1 Bujkiewicz S.

1 Eaves L.

1 Fowler D.

1 Fromhold T.

1 Henini M.

1 Krokhin A.

1 Lewenstein M.

1 Neumann A.

1 Patanè A.

1 Raymer M. G.

1 Sankeshwar N.

1 Sheard F.

1 Sherwood D.

1 Smithey D. T.

1 Stapleton S.

1 Wilkinson P.

1 You L.

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Quantum States and Number-Phase Uncertainty Relations Measured by Optical Homodyne Tomography

Quantum Optics of a Bose-Einstein Condensate

Stochastic Carrier Dynamics in Semiconductor Superlattices