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.
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.
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.
ABSTRACT This thesis explores the photon-number characteristics and quantum communication po tential of superposed squeezed vacuum states, emphasizing their relevance to Quantum Key Distribution (QKD). The analysis investigates how statistical indicators of the light field—such as the average photon number and its fluctuations—reveal nonclassical be havior, including reduced quadrature noise and altered photon-number distributions that support efficient quantum encoding. Secure communication performance is evaluated through conditional probability methods and mutual information calculations, while Q function phase-space representations illustrate interference patterns and deformation in amplitude distributions arising from squeezing and photon correlations. A Gaussian se curity model is applied to estimate the Holevo bound and quantify possible information gained by an eavesdropper. MATLAB simulations demonstrate that tuning the squeez ing strength and superposition parameters enhances the achievable key rate, showing that superposed squeezed states exhibit increased resilience to channel loss and common quantum attacks, making them strong candidates for secure, low-photon, long-distance QKDapplications. Keywords:-Photon number variation,Q-function analysis, Quadrature squeezing, Quantum Key Distribution (QKD),Secret key rate analysis,Superposed squeezed vac uum states i
ABSTRACT This thesis explores the photon-number characteristics and quantum communication po tential of superposed squeezed vacuum states, emphasizing their relevance to Quantum Key Distribution (QKD). The analysis investigates how statistical indicators of the light field—such as the average photon number and its fluctuations—reveal nonclassical be havior, including reduced quadrature noise and altered photon-number distributions that support efficient quantum encoding. Secure communication performance is evaluated through conditional probability methods and mutual information calculations, while Q function phase-space representations illustrate interference patterns and deformation in amplitude distributions arising from squeezing and photon correlations. A Gaussian se curity model is applied to estimate the Holevo bound and quantify possible information gained by an eavesdropper. MATLAB simulations demonstrate that tuning the squeez ing strength and superposition parameters enhances the achievable key rate, showing that superposed squeezed states exhibit increased resilience to channel loss and common quantum attacks, making them strong candidates for secure, low-photon, long-distance QKDapplications. Keywords:-Photon number variation,Q-function analysis, Quadrature squeezing, Quantum Key Distribution (QKD),Secret key rate analysis,Superposed squeezed vac uum states i
Generation of nonclassical lights, such as photon-number squeezed states and quadrature-phase squeezed state, is required to realize optical communications and accurate measurements at sub-shot-noise levels. Among a variety of schemes, the direct generation of sub-Poissonian photon fluxes from semiconductor light emitters has been attracting much attention because of the simplicity of experimental arrangement, the low energy consumption, the possibility of a large degree of noise suppression, and the compatibility with modern communication system. In this presentation, we demonstrate the experimental results of generation of sub-Poissonian photon fluxes in an integrated light-emitter/detector system. It is shown that the pump-noise-suppression owing to the macroscopic Coulomb blockade effect can work well even when a superlattice alloylike material is used.
In this dissertation measurements are presented that extend our understanding of the important noise processes involved in the semiconductor laser generation of photon-number squeezed light. Strong sub-shot noise correlations between photon-number fluctuations on orthogonal polarization axes are observed in the output of a low temperature injection-locked quantum-well laser. Such polarization dependent effects are accounted for by intrinsic correlations generated in the laser gain medium and polarization mixing due to birefringence. Using polarization preserving balanced homodyne detection, up to 4.5 dB of photon-number squeezing is reported, which is within 95% of the expected maximum squeezing based on the device quantum efficiency. The work in this dissertation demonstrates the application of such nonclassical fields to practical measurements that achieve sub-shot noise sensitivity. Coherent nonlinear optical spectroscopy with a photon-number squeezed probe field is used to measure the Urbach tail and exciton resonances in a GaAs/AlGaAs multiple quantum well with sensitivity below the semiclassical shot-noise limit. Direct drive current modulation of an injection-locked room temperature laser results in a nonclassical amplitude modulated field with a signal to noise ratio that exceeds the maximum ratio permitted for a classical source under equivalent modulation conditions.
The origin of quantum noise is addressed and it can be eliminated when the quantum state is optimally prepared for the single measured observable. Minimum uncertainty states are reviewed using Q (α) -representation, which include squeezed states and number-phase minimum uncertainty states. Squeezing is a concept of trading quantum uncertainties between two conjugate observables to optimize the state for the measurement. Need for optical nonlinearity to achieve squeezing is induced. Principles and experimental results for squeezing quadrature amplitude and photon number are delineated. Applications to optical communications and optical precision measurement are briefly stated.