R. R. Puri

Mathematical methods of quantum optics

1. Basic Quantum Mechanics.- 1.1 Postulates of Quantum Mechanics.- 1.1.1 Postulate 1.- 1.1.2 Postulate 2.- 1.1.3 Postulate 3.- 1.1.4 Postulate 4.- 1.1.5 Postulate 5.- 1.2 Geometric Phase.- 1.2.1 Geometric Phase of a Harmonic Oscillator.- 1.2.2 Geometric Phase of a Two-Level System.- 1.2.3 Geometric Phase in Adiabatic Evolution.- 1.3 Time-Dependent Approximation Method.- 1.4 Quantum Mechanics of a Composite System.- 1.5 Quantum Mechanics of a Subsystem and Density Operator.- 1.6 Systems of One and Two Spin-1/2s.- 1.7 Wave-Particle Duality.- 1.8 Measurement Postulate and Paradoxes of Quantum Theory.- 1.8.1 The Measurement Problem.- 1.8.2 Schrodingers Cat Paradox.- 1.8.3 EPR Paradox.- 1.9 Local Hidden Variables Theory.- 2. Algebra of the Exponential Operator.- 2.1 Parametric Differentiation of the Exponential.- 2.2 Exponential of a Finite-Dimensional Operator.- 2.3 Lie Algebraic Similarity Transformations.- 2.3.1 Harmonic Oscillator Algebra.- 2.3.2 The SU(2) Algebra.- 2.3.3 The SU(1,1) Algebra.- 2.3.4 The SU(m) Algebra.- 2.3.5 The SU(m, n) Algebra.- 2.4 Disentangling an Exponential.- 2.4.1 The Harmonic Oscillator Algebra.- 2.4.2 The SU(2) Algebra.- 2.4.3 SU(1,1) Algebra.- 2.5 Time-Ordered Exponential Integral.- 2.5.1 Harmonic Oscillator Algebra.- 2.5.2 SU (2) Algebra.- 2.5.3 The SU(1,1) Algebra.- 3. Representations of Some Lie Algebras.- 3.1 Representation by Eigenvectors and Group Parameters.- 3.1.1 Bases Constituted by Eigenvectors.- 3.1.2 Bases Labeled by Group Parameters.- 3.2 Representations of Harmonic Oscillator Algebra.- 3.2.1 Orthonormal Bases.- 3.2.2 Minimum Uncertainty Coherent States.- 3.3 Representations of SU(2).- 3.3.1 Orthonormal Representation.- 3.3.2 Minimum Uncertainty Coherent States.- 3.4 Representations of SU(1, 1).- 3.4.1 Orthonormal Bases.- 3.4.2 Minimum Uncertainty Coherent States.- 4. Quasiprobabilities and Non-classical States.- 4.1 Phase Space Distribution Functions.- 4.2 Phase Space Representation of Spins.- 4.3 Quasiprobabilitiy Distributions for Eigenvalues of Spin Components.- 4.4 Classical and Non-classical States.- 4.4.1 Non-classical States of Electromagnetic Field.- 4.4.2 Non-classical States of Spin-1/2s.- 5. Theory of Stochastic Processes.- 5.1 Probability Distributions.- 5.2 Markov Processes.- 5.3 Detailed Balance.- 5.4 Liouville and Fokker-Planck Equations.- 5.4.1 Liouville Equation.- 5.4.2 The Fokker-Planck Equation.- 5.5 Stochastic Differential Equations.- 5.6 Linear Equations with Additive Noise.- 5.7 Linear Equations with Multiplicative Noise.- 5.7.1 Univariate Linear Multiplicative Stochastic Differential Equations.- 5.7.2 Multivariate Linear Multiplicative Stochastic Differential Equations.- 5.8 The Poisson Process.- 5.9 Stochastic Differential Equation Driven by Random Telegraph Noise.- 6. The Electromagnetic Field.- 6.1 Free Classical Field.- 6.2 Field Quantization.- 6.3 Statistical Properties of Classical Field.- 6.3.1 First-Order Correlation Function.- 6.3.2 Second-Order Correlation Function.- 6.3.3 Higher-Order Correlations.- 6.3.4 Stable and Chaotic Fields.- 6.4 Statistical Properties of Quantized Field.- 6.4.1 First-Order Correlation.- 6.4.2 Second-Order Correlation.- 6.4.3 Quantized Coherent and Thermal Fields.- 6.5 Homodvned Detection.- 6.6 Spectrum.- 7. Atom-Field Interaction Hamiltonians.- 7.1 Dipole Interaction.- 7.2 Rotating Wave and Resonance Approximations.- 7.3 Two-Level Atom.- 7.4 Three-Level Atom.- 7.5 Effective Two-Level Atom.- 7.6 Multi-channel Models.- 7.7 Parametric Processes.- 7.8 Cavity QED.- 7.9 Moving Atom.- 8. Quantum Theory of Damping.- 8.1 The Master Equation.- 8.2 Solving a Master Equation.- 8.3 Multi-Time Average of System Operators.- 8.4 Bath of Harmonic Oscillators.- 8.4.1 Thermal Reservoir.- 8.4.2 Squeezed Reservoir.- 8.4.3 Reservoir of the Electromagnetic Field.- 8.5 Master Equation for a Harmonic Oscillator.- 8.6 Master Equation for Two-Level Atoms.- 8.6.1 Two-Level Atom in a Monochromatic Field.- 8.6.2 Collisional Damping.- 8.7 aster Equation for a Three-Level Atom.- 8.8 Master Equation for Field Interacting with a Reservoir of Atoms.- 9. Linear and Nonlinear Response of a System in an External Field.- 9.1 Steady State of a System in an External Field.- 9.2 Optical Susceptibility.- 9.3 Rate of Absorption of Energy.- 9.4 Response in a Fluctuating Field.- 10. Solution of Linear Equations: Method of Eigenvector Expansion.- 10.1 Eigenvalues and Eigenvectors.- 10.2 Generalized Eigenvalues and Eigenvectors.- 10.3 Solution of Two-Term Difference-Differential Equation.- 10.4 Exactly Solvable Two- and Three-Term Recursion Relations.- 10.4.1 Two-Term Recursion Relations.- 10.4.2 Three-Term Recursion Relations.- 11. Two-Level and Three-Level Hamiltonian Systems.- 11.1 Exactly Solvable Two-Level Systems.- 11.1.1 Time-Independent Detuning and Coupling.- 11.1.2 On-Resonant Real Time-Dependent Coupling.- 11.1.3 Fluctuating Coupling.- 11.2 N Two-Level Atoms in a Quantized Field.- 11.3 Exactly Solvable Three-Level Systems.- 11.4 Effective Two-Level Approximation.- 12. Dissipative Atomic Systems.- 12.1 Two-Level Atom in a Quasimonochromatic Field.- 12.1.1 Time-Dependent Evolution Operator Reducible to SU(2).- 12.1.2 Time-Independent Evolution Operator.- 12.1.3 Nonlinear Response in a Bichromatic Field.- 12.2 N Two-Level Atoms in a Monochromatic Field.- 12.3 Two-Level Atoms in a Fluctuating Field.- 12.4 Driven Three-Level Atom.- 13. Dissipative Field Dynamics.- 13.1 Down-Conversion in a Damped Cavity.- 13.1.1 Averages and Variances of the Cavity Field Operators.- 13.1.2 Density Matrix.- 13.2 Field Interacting with a Two-Photon Reservoir.- 13.2.1 Two-Photon Absorption.- 13.2.2 Two-Photon Generation and Absorption.- 13.3 Reservoir in the Lambda Configuration.- 14. Dissipative Cavity QED.- 14.1 Two-Level Atoms in a Single-Mode Cavity.- 14.2 Strong Atom-Field Coupling.- 14.2.1 Single Two-Level Atom.- 14.3 Response to an External Field.- 14.3.1 Linear Response to a Monochromatic Field.- 14.3.2 Nonlinear Response to a Bichromatic Field.- 14.4 The Micromaser.- 14.4.1 Density Operator of the Field.- 14.4.2 Two-Level Atomic Micromaser.- 14.4.3 Atomic Statistics.- Appendices.- A. Some Mathematical Formulae.- B. Hypergeometric Equation.- C. Solution of Twoand Three-Dimensional Linear Equations.- D. Roots of a Polynomial.- References.

Quantum electrodynamics of an atom making two-photon transitions in an ideal cavity

It is shown that a single atom making two-photon transitions in an ideal cavity (Q = ∞) in the presence of an initial coherent state field will, as expected, continue to show the collapses and revivals of atomic inversion and the intensity–intensity correlation of the field; however, these collapses and revivals are both compact and regular, in contrast to the one-photon case. This is because, although the several Rabi frequencies involved are incommensurate, for the two-photon case, unlike for the one-photon problem, they become commensurate in the limit of intense field. We derive analytic expressions for the atomic inversion and the intensity–intensity correlation in the case of direct, as well as homodyned, detection of the intracavity field. The effects of the Stark shift are discussed.

Exact steady-state density operator for a collective atomic system in an external field

Abstract An exact steady-state density operator is obtained for a model describing the collective behaviour of a system of N two-level atoms driven by a classical field. This is used to obtain the exact steady-state expectation value of the atomic population difference for any N .

Quantum theory of recent observations on Rydberg atoms in low-Q cavities

Recent experimental observations of the cooperative behaviour of sodium Rydberg atoms interacting with a thermal field in a low-Q cavity are accounted for quantum theoretically by using the driven Dicke model. Substantially changed observations in high-Q cavities are predicted.

Intensity fluctuations in a driven Dicke model

Exact analytic results for the steady-state atomic correlation functions of arbitrary order n are given for a system of N superimposed two-level atoms (the Dicke model) collectively interacting with an imposed C.W. laser field. Photon statistical studies through the normalised intensity-intensity correlation function, g(2)(0), show that when both N and the driving field become large, g(2)(0) → 1.2. This compares with an earlier approximated calculation1) which allows an independent atomic decay mechanism giving rise to g(2)(0) ≈ 2. Cooperative interactions thus reduce intensity fluctuations. Photon anti-bunching occurs for finite N. There is a second-order phase transition critical bifurcation point in a thermodynamic limit in which N → ∞; a critical exponent is determined.

Non-resonant effects in the fluorescent Dicke model. I. Exact steady state analysis

The exact steady state solution for the reduced atomic density operator for a model of N identical two-level atoms occupying the same site (the Dicke model) and driven by a CW off-resonant laser field is presented. Exact expressions are given for the atomic observables and atomic correlation functions of arbitrary order. Exact thermodynamic analysis (N to infinity ) shows that the critical phase transition behaviour found in the resonant case is destroyed due to non-resonant effects. For large N and increasing detuning parameter, quantum fluctuations tend to vanish and hence the atomic observables tend to assume their semiclassical values. Also it is found that for a fixed arbitrary detuning parameter and increasing N these fluctuations disappear for the whole range of the driving field strength. The authors explain why it is not possible in the limit N to infinity to recover the correct asymptotic limit for the resonant case from the results of the dispersive case.

Time-dependent invariants and stable coherent states

Abstract The time evolution of a coherent state is discussed using an explicitly time-dependent invariant of the underlying hamiltonian. It is shown that a stable coherent state is an eigenstate of such an invariant.

Incoherently driven Dicke model

The exact steady-state solution for the reduced atomic density operator for a model system of N identical two-level atoms confined to a single site (the Dicke model) and driven by a totally incoherent broad-band (chaotic) field is derived through the equivalent Fokker-Planck equation of the system. Steady-state values of the atomic observables, higher moments and atomic fluctuations are calculated for an arbitrary N and an arbitrary field strength. It is shown that when the chaotic field is a thermal (black-body) field the atomic system is driven into a steady relative occupation number that obeys the Boltzmann distribution law only for N=1. (The same result for N>1 atoms can be reached only if the cooperative interactions between the atoms are ignored.) In the thermodynamic limit N to infinity there is no critical behaviour in contrast to the resonant coherently driven case. It is also shown that semiclassical (direct) factorisation of the equations of motion does not lead to the correct results for the N to infinity limit of the exact quantum case. Within the exact theory numerical results for finite N (<or=100) are presented for the time-dependent expectation values of the atomic operators, the intensity and the intensity autocorrelation function. Superradiant pulses are emitted by N initially inverted atoms but as the incident intensity is increased this superradiant behaviour is obscured. The steady-state fluorescence spectrum is a single Lorentzian of width proportional to N in the weak-field case. In the strong-field case the spectrum is insensitive to the number of atoms and the result is similar to the one-atom situation. Photon bunching and antibunching effects are investigated for the weak- and strong-field limits. When the chaotic driving field is simply a single-mode thermal field the approach to atomic saturation is delayed in comparison with the case of the broad-band chaotic field.

Dispersion in the driven dicke model

Abstract An exact steady state solution for the atomic density operator is obtained for a model of N identical superimposed two- level atoms (the Dicke model) driven by a cw off-resonance laser field. Exact expressions are given then for the atomic observables and their fluctuations and for the atomic correlation functions for any N. The results show that the second order phase transition critical bifurcation point found in the resonant case and for N → ∞ disappears due to the dispersive (non- resonant) effects. This is confirmed, further, by an exact semiclassical analysis of the governing equations of motion.

Monitoring quantum effects in cavity electrodynamics by atoms in semiclassical dressed states

Field quantization effects in cavity electrodynamics can be isolated by sending through the cavity those atoms prepared initially in semiclassical dressed states. Under such initial conditions the fully quantized theory predicts irregular evolution, whereas the semiclassical and neoclassical theories predict, respectively, no dynamical evolution and regular periodic evolution.