Squeezed states possess an unequal noise division between the quadrature components, a, and â2, yet stiil satisfy a minimum uncertainty product 〈 Δ a 1 2 〉 〈 Δ a 2 2 〉 = 1 / 16. This nonclassical behavior has stimulated great interest in the generation, detection, and application ot squeezed states.
Electromagnetic fields, with the noise on one quadrature component reduced to below the quantum mechanical zero-point fluctuation level and the noise on the other quadrature component enhanced to above it, are currently of great interest in quantum optics because of their potential applications to various precision measurements. Such squeezed states of light are usually produced by imposing nonlinear unitary evolution on coherent (or vacuum) states. On the other hand, squeezed states with reduced photon number noise and enhanced phase noise are generated directly by a constant current-driven semiconductor laser. This is the simplest scheme for the generation of nonclassical light, and so far it has yielded the largest quantum noise reduction. The mutual coupling between a lasing junction and an external electrical circuit provides opportunities for exploring the macroscopic and microscopic quantum effects in open systems.
Squeezed states of light are minimum uncertainty states for which the mean square fluctuations in phase and in quadrature with respect to a reference signal are unequal. Among other interesting properties, they provide improved sensitivity of optical interferometric phase measurements. To understand this potential, one must note that quantum theory imposes measurement uncertainty only on a pair of noncommuting variables; the measurement of any one quantum observable could be done with no uncertainty.>
Recently a number of laboratories have demonstrated the generation of squeezed light, a new kind of light which in some of its aspects exhibits less quantum noise then coherent light. Here a description will be given of how such light is generated and detected. With the successful generation and detection of squeezed light by a number of laboratories1-5 a new degree of control over the quantum statistics of light has been achieved. Light can now be generated which, in some of its aspects, has less quantum noise than coherent light. Such light may find applications in optical communications and in sensitive and precision measurement. Here a description will be given of how squeezed light is generated and detected.6-8 The discussion will be restricted to what is called "quadrature squeezing". The electric field operator for a single mode of the electromagnetic field can be written in the form
Squeezed states of light have found importance in quantum cryptography due to the no-cloning theorem which prevents two states from being identical to each other. The quantum state with quadrature operators X1 and X2 can be visualized as a point in phase space with the center being l angle X1 r angle, l angle X2 r angle surrounded by an error region which satisfies the minimum uncertainty product l angle Delta X [1 over 2] r angle l angle Delta X [2 over2] r angle=1/16. These states are intrinsically secure since one needs to know which quadrature the measurement is to be made and any attempt to measure the wrong quadratures with arbitrary accuracy would disturb the message. Of course, the eavesdropper cannot simultaneously measure both quadratures with infinite precision for each. This thesis describes a method that not only encodes information in the amplitudes of the quadratures alone but also in the uncertainty of those states. One example of squeezed light is the number-phase squeezed state which satisfying the uncertainity relation l angle Delta n [superscript] 2 r angle l angle Delta phi [superscript] 2 r angle=1/4. An implementation is demonstrated where the information is encoded only in the photon number uncertainity and the phase variable is ignored.The barrier regulation mechanisms such as macroscopic coulomb blockade in semiconductor junction diodes are responsible for generating photon fluxes with penetration below the standard quantum limit(shot noise level). The thesis describes a comprehensive quantum mechanical Langevin model which details the various mechanisms responsible for producing photon number squeezing from the thermionic emission to the diffusion current limits. Quantities such as the pump fluctuations and cross correlation spectral densities are studied under constant current and constant voltage conditions. The research investigates the generation of photon number squeezed light from high efficiency light emitting diodes. A measurement setup for subshot noise is constructed and each stage is properly calibrated. Experiments were performed to determine the squeezing spectra and Fanofactors for the L2656 and the L9337 high efficiency LEDs. The L9337 produces a squeezing of 1.5dB below the shot noise level over a bandwidth of 25Mhz, the largest known penetration at room temperature. The quantum stochastic communicator is also demonstrated. The research shows that the switching elements used in the modulation of the electrical bias which in turn affect the regulation mechanisms do not affect the statistics of the emitted light under certain conditions. The decoding of the time varying variances is achieved by using time frequency analysis with the aid of the spectrum analyzer.