A mirror in vacuum is submitted to a radiation pressure exerted by scattered fields. It is known that the resulting mean force is zero for a motionless mirror, but not for a mirror moving with a non-uniform acceleration. We show here that this force results from a motional modification of the field scattering while being associated with the fluctuations of the radiation pressure on a motionless mirror. We consider the case of a scalar field in a two-dimensional spacetime and characterize the scattering upon the mirror by frequency dependent transmissivity and reflectivity functions obeying unitarity, causality and high frequency transparency conditions. We derive causal expressions for dissipation and fluctuations and exhibit their relation for any stationary input. We recover the known damping force at the limit of a perfect mirror in vacuum. Finally, we interpret the force as a mechanical signature of the squeezing effect associated with the mirror's motion.
A combination of less frequent criticism with positive investigations has resulted in the substitution of group theoretic considerations by a simpler quantum mechanical model, has taken into account homodyne and heterodyne detection schemes, and proceeded by an analysis of phase data processing. Limiting procedures in s-phase formalisms have been provided concentrating on the Wigner function for number and ideal phase. The Wigner function for number and realistic phase has been expressed by closed formulae along with the antinormal phase distributions.
Aspects of lasing without inversion (LWI) have been the subject of spirited debate. Analytical solutions are here presented which provide a useful tool for resolving many of the conundrums and also provide new insights into the physics of the problem. The presentation is written for the student with some background in laser physics but not LWI. Some of the material is therefore in the nature of a review.
The properties of the displaced Fock states \alpha,n> = D(alpha,alpha*)\n>, (alpha-complex numbers, D(alpha,alpha*) displacement operators, n = 0, 1, 2,...) are systematically investigated with emphasis on the connections to the Heisenberg-Weyl group and to its irreducible representations. The displaced Fock states comprise the coherent states \alpha> = \alpha,0> as well as the Fock states \n> = \0,n> as particular cases. An orthocompleteness relation for the displaced Fock states in the form of the area integral of the operators \alpha,m>
The Shapiro-Wagner phase measurement is addressed here. It is clarified that this concept includes an infinite number of operator realizations of quantum phase measurements, which may be characterized using polar and spectral decomposition. For accurate phase measurement, the regimes of ideal and optimized phase resolution are specified. The former is equivalent to the Susskind-Glogower or Hermitian phase concepts and needs infinite energy on the auxiliary input port. The ultimate phase resolution cannot surpass the limit 1/n, n being the total average number of photons entering both the signal and image input ports.
We derive an amplification condition which generalizes the traditional population inversion requirement for the basic schemes of inversionless amplification. We develop a self-consistent quantum approach for the description of such schemes and demonstrate the limitations of the traditional phenomenological approach.
The term quantum beats refers to a superposed oscillatory behaviour in the light intensity emitted by some suddenly excited atomic systems in their subsequent decay. In this paper we reinvestigate quantum beats for systems where two upper levels may decay to a common ground state by using the recently developed approach of quantum jumps. The treatment turns out to be very simple and intuitive. It gives explicit expressions for the time-dependent intensity of the radiating system and allows us to exhibit several phenomena which so far seem to have been overlooked. We show that quantum beats may also occur if only one of the upper levels is initially excited, a superposition is not needed. A possible experimental set-up for the verification of this effect is proposed. It is also shown that in some cases the beat frequency may differ considerably from the separation deltaomega of the upper levels. For equal Einstein coefficients of the upper levels the beats are shown to be unexpectedly absent for small deltaomega.
In recent years much attention has been paid to the quantized evolution of the centre-of-mass momentum and position of ultracold atoms in light fields. We consider the effects resulting from the quantization of the external angular momentum variables. We investigate how spin and orbital angular momentum of light are transferred to internal and external angular momentum of an atom in dipole and quadrupole transitions.
A possible realistic implementation of a method for interaction-free measurements, due to Elitzur and Vaidman, is proposed and discussed. It is argued that the effect can be observed in an optical laboratory
Theoretical methods for treating propagation in quantum optics are developed, in which the momentum operator is used in addition to the Hamiltonian. A quantum mechanical analysis is given for various physical systems which include amplification and coupling between electromagnetic modes. A quantum mechanical theory for distributed feedback lasers (DFL) is described.
We review the effects of density dependent near dipole-dipole, or local field, interactions on lasing without inversion. In particular, we consider the nonlinear behaviour of the macroscopic electric susceptibility of a dense, coherently prepared, three-level LAMBDA system. For certain values of the atomic density, we observe enhancement of the absorptionless index of refraction and inversionless gain by more than two orders of magnitude. We also predict a piezophotonic switching effect whereby a small change in density induces the system to flip from a strong absorber into a local field enhanced inversionless amplifier.
A theoretical review of the use of optical solitons in fibres for high speed communication is presented with emphasis on recent progress in soliton control. An optical soliton is a pulse of light in a fibre produced by a balance of group velocity dispersion and cubic non-linearity. Twenty years after its discovery, optical solitons are rapidly attracting interest from technical as well as scientific communities thanks to progress in coherent light source, fibre amplifier and other photonic devices and surprising agreement of the theoretical predictions with experimental observations.
Starting from a convenient measure for the phase uncertainty delta-phi, a rigorous solution to the variational problem in which (delta-phi)2 is minimized under the constraint that the mean photon number N is held fixed, was found. In an approximation valid for large values of N, closed-form expressions for both (delta-phi)2 and the variance of the photon number (DELTA-n)2 were obtained. In the final result, our approximation is very similar to an approximation scheme recently discussed by Summy and Pegg. The phase uncertainty for the phase optimized states is found to decrease as (N + 1)-1 with growing N.
We present an exact expression for the joint count probability in an eight-port homodyne detector used in a recent proposal for a phase measurement by Noh et al. For a strong local oscillator we relate this joint count probability to the Q-function of the arbitrary input state. This Q-function integrated over radius is the phase distribution corresponding to the phase operators of Noh et al.