Two-mode Fock State Research Articles

Projection operators for asymmetric two-mode coherent states and two-mode Fock states

Operators play an important role in the formalism of quantum mechanics. By means of the technique of integration within an ordered product of operators and Dirac notation, we analytically prove that a new kind of asymmetric two-mode projection integral operator and another asymmetric two-mode Fock state projection summation operator are equal to the same Hermitian operator. For such Hermitian operator, we also rigorously demonstrate it corresponds to a parity measurement of a two-mode quantum state after passing through a beam splitter. The method used in this work provides a good exercise in quantum mechanics at the graduate level.

Construction of the Superposition of Displaced Fock States and Entangled Displaced Fock States

In this paper, at first we will construct the superposition of two displaced Fock states and two-mode entangled displaced Fock states mathematically by presenting theoretical methods. In these methods, we will introduce new operators using the parity and displacement operators. It will be observed that the superposition of two displaced Fock states and two-mode entangled displaced Fock states are constructed via the action of the introduced operators on one-mode and two-mode Fock states, respectively. Next, we will show that the presented methods have the potential ability to produce the superposition consist of more than two displaced Fock states and multi-mode entangled displaced Fock states, too.

Quantum Control of the States of Light in a Mach-Zehnder Interferometer

The experiment proposed by Elitzur and Vaidman is modified by replacing the fully absorbing obstacle (the ‘bomb’) with a non-linear optical medium. In this form the involved Mach-Zehnder interferometer works as a quantum beam splitter that produces NOON states which can be controlled if the input is the appropriate linear combination of two-mode Fock states.

Complex Wavelet Transform of the Two-mode Quantum States

By employing the bipartite entangled state representation and the technique of integration within an ordered product of operators, the classical complex wavelet transform of a complex signal function can be recast to a matrix element of the squeezing-displacing operator U2(μ, σ) between the mother wavelet vector 〈ψ| and the two-mode quantum state vector |f〉 to be transformed. 〈ψ|U2(μ, σ)|f〉 can be considered as the spectrum for analyzing the two-mode quantum state |f〉. In this way, for some typical two-mode quantum states, such as two-mode coherent state and two-mode Fock state, we derive the complex wavelet transform spectrum and carry out the numerical calculation. This kind of wavelet-transform spectrum can be used to recognize quantum states.

Effects of cavity-field statistics on atomic entanglement in a two-mode Jaynes–Cummings model with intensity-dependent coupling

We study the entanglement properties of a pair of two-level Rydberg atoms passing one after another into a lossless cavity with two modes. The atoms interact with the cavity field via an intensity-dependent, non-degenerate two-photon transition. The initial joint state of two successive atoms that enter the cavity is unentangled. Interactions mediated by the two-mode cavity photon field result in the final two-atom mixed entangled type state. The entanglement of formation of the joint two-atom state as a function of the Rabi angle, gt, is calculated for the two-mode Fock state field, coherent field, and thermal field, respectively, inside the cavity. The change in the magnitude of atomic entanglement with cavity photon number in two modes has been studied.

Filtering of the absolute value of photon-number difference for two-mode macroscopic quantum superpositions

We discuss a device capable of filtering out two-mode states of light with mode populations differing by more than a certain threshold, while not revealing which mode is more populated. It would allow engineering of macroscopic quantum states of light in a way which is preserving specific superpositions. As a result, it would enhance optical phase estimation with these states as well as distinguishability of "macroscopic" qubits. We propose an optical scheme, which is a relatively simple, albeit non-ideal, operational implementation of such a filter. It uses tapping of the original polarization two-mode field, with a polarization neutral beam splitter of low reflectivity. Next, the reflected beams are suitably interfered on a polarizing beam splitter. It is oriented such that it selects unbiased polarization modes with respect to the original ones. The more an incoming two-mode Fock state is unequally populated, the more the polarizing beam splitter output modes are equally populated. This effect is especially pronounced for highly populated states. Additionally, for such states we expect strong population correlations between the original fields and the tapped one. Thus, after a photon-number measurement of the polarizing beam splitter outputs, a feed-forward loop can be used to let through a shutter the field, which was transmitted by the tapping beam splitter. This happens only if the counts at the outputs are roughly equal. In such a case, the transmitted field differs strongly in occupation number of the two modes, while information on which mode is more populated is non-existent (a necessary condition for preserving superpositions).

Calculation of Gaussian Perturbation on Two Harmonic Oscillators byVirtue of Entangled State Representation

The exact expressions of Gaussian-perturbation matrix elements inone- and two-mode Fock states are derived by virtue of the technique ofintegration within an ordered product of operators and theentangled state representation. It turns out that the matrixelements are just related to Gegenbauer polynomial and Hypergeometricfunction respectively. The 1st- and 2nd-order corrections tothe energy levels and the 1st-order correctionto wavefunctions of harmonic oscillator are deduced.

Heisenberg-limited polarimetry using multiphoton two-mode Fock states

We show that appropriate nonclassical photon states can attain Heisenberg-limited sensitivity in polarimetric measurements, in which the squared amplitudes of the photon states are measured. These photon states, which can be constructed from the two-mode Fock states, are found as the eigenstates of a Hermitian operator, which is closely related to the quantum Stokes operators. The algebraic property of the Hermitian operator governs the interferometric behavior in polarimetric interactions and provides the frequency of the interferometric fringes scaled by the total number of photons of the state. Thus, the polarimetry is able to achieve Heisenberg-limited sensitivity.

Two-Variable Hermite Function as Quantum Entanglement of HarmonicOscillator's Wave Functions

We reveal that the two-variable Hermite function hm,n, whichis the generalized Bargmann representation of the two-mode Fock state, involvesquantum entanglement of harmonic oscillator's wave functions. The Schmidtdecomposition of hm,n is derived. It also turns out that hm,n canbe generated by windowed Fourier transform of the single-variable Hermitefunctions. As an application, the wave function of the two-variable Hermitepolynomial state S(r)Hm,n(μa1†,μa2†)|00⟩, which is the minimum uncertaintystate for sum squeezing, in ⟨η| representationis calculated.

On Common Eigenvector of Parametric Interaction Hamiltonian andNumber-Difference Operator Derived by Virtue of Entangled StateRepresentation

By virtue of the properties of bipartite entangled state representation wederive the common eigenvector of the parametric Hamiltonian and the two-modenumber-difference operator. This eigenvector is superposition of somedefinite two-mode Fock states with the coefficients being proportional tohypergeometric functions. The Gauss contiguous relation of hypergeometricfunctions is used to confirm the formal solution.

Entanglement by linearSU(2) transformations: generation and evolution of quantum vortex states

We consider the evolution of a two-mode system of bosons under the action of a Hamiltonian that generates linear SU(2) transformations. The Hamiltonian is generic in that it represents a host of entanglement mechanisms, which can thus be treated in a unified way. We start by solving the quantum dynamics analytically when the system is initially in a Fock state. We show how the two modes get entangled by evolution to produce a coherent superposition of vortex states in general, and a single vortex state under certain conditions. The degree of entanglement between the modes is measured by finding the explicit analytical dependence of the Von Neumann entropy on the system parameters. The reduced state of each mode is analyzed by means of its correlation function and spatial coherence function. Remarkably, our analysis is shown to be equally as valid for a variety of initial states that can be prepared from a two-mode Fock state via a unitary transformation and for which the results can be obtained by mere inspection of the corresponding results for an initial Fock state. As an example, we consider a quantum vortex as the initial state and also find conditions for its revival and charge conjugation. While studying the evolution of the initial vortex state, we have encountered and explained an interesting situation in which the entropy of the system does not evolve whereas its wave function does. Although the modal concept has been used throughout the paper, it is important to note that the theory is equally applicable for a two-particle system in which each particle is represented by its bosonic creation and annihilation operators.

Generalized Bargmann Representation of Spin Coherent State**The project supported by National Natural Science Foundation of China under Grant No. 10175057

Based on the conclusion that the generalized Bargmann representation of a two-mode Fock state is a two-variable Hermite polynomial function [Hong-Yi Fan and Jun-hua Chen, Phys. Lett. A303 (2002) 311] we derive the generalized Bargmann representation of the spin coherent state and some new relations in the generalized function space.

EPR entangled state and generalized Bargmann transformation

Abstract In similar to the relation between the coherent state and the Bargmann transform, we find a generalized Bargmann transformation naturally accompanying Einstein–Podolsky–Rosen (EPR) entangled state of continuous variables. The new Bargmann transform kernel is introduced which can naturally lead to the entangled state. The generalized Bargmann representation of two-mode Fock state is a two-variable Hermite polynomial.

Wehrl's entropy and a measure of intermode correlations in phase space

The properties of the entangled pure states in phase space are analysed using the classical entropy introduced by Wehrl. The general entropy inequalities for non-entangled pure states are derived, which are violated by any entangled state. To measure the strength of intermode correlations in phase space the parameters related to these inequalities are proposed. As an example we study the correlations between amplitudes and phases for two-mode Fock states. We find that the amplitudes as well as phases of different modes are correlated. It is also shown that the degree of the intermode correlation strongly depends on the photon number difference in two-mode Fock states.

Quantum Nondemolition Measurement of Photon-Number Distribution for a Two-Mode Field**The project supported by Science Research Foundation of Education Committee of Fujian Province and Funds from Fuzhou University

We propose a quantum nondemolition measurement of the photon-number distribution for a two-mode cavity field. In the scheme two sequences of two-level atoms interact dispersively with the respective cavity modes and resonantly with two classical fields, and then are detected continually. The field finally reduces to a two-mode Fock state. The probability of collapsing to a given Fock state is determined by the initial photon-number distribution. The scheme can be easily generalized to a field with N modes.

Vibrational pair cat states.

We propose a scheme for generating mesoscopic superpositions of two distinguishable pair coherent states of motion in a two-dimensional ion trap. In our scheme, the trapped ion is excited bichromatically by five laser beams along different directions in the X-Y plane of the ion trap. Four of these have the same frequency and can be derived from the same source, reducing the demands on the experimentalist. We show that if the initial vibrational state is given by a two-mode Fock state, as demonstrated in recent experiments, these highly correlated two-mode ``Schr\"odinger cat'' states are realized when the system reaches its steady state, which is indicated by the extinction of the fluorescence emitted by the ion. \textcopyright{} 1996 The American Physical Society.

Dark pair coherent states of the motion of a trapped ion.

We propose a scheme for generating vibrational pair coherent states of the motion of an ion in a two-dimensional trap. In our scheme, the trapped ion is excited bichromatically by three laser beams along different directions in the X-Y plane of the ion trap. We show that if the initial vibrational state is given by a two-mode Fock state, the final steady state, indicated by the extinction of the fluorescence emitted by the ion, is a pure state. The motional state of the ion in the equilibrium realizes that of the highly-correlated pair coherent state.

Further investigations of the operationally defined quantum phase.

The formalism that we have previously developed for the phase difference between two quantized electromagnetic fields, which is intimately connected with the measurement process, is explored further, both theoretically and experimentally. We calculate the higher moments of the measured cosine and sine operators for certain two-mode Fock states \ensuremath{\Vert}${\mathit{n}}_{1}$,${\mathit{n}}_{2}$〉, and show how the measurement itself exerts a bias on the outcome. We find that the corresponding phase difference becomes uniform over the interval 0 to 2\ensuremath{\pi} only in the limit ${\mathit{n}}_{1}$,${\mathit{n}}_{2}$\ensuremath{\rightarrow}\ensuremath{\infty}. On the other hand, the phase difference associated with the product of a coherent state \ensuremath{\Vert}v〉 with a Fock state can be random for large \ensuremath{\Vert}v\ensuremath{\Vert}, because of the availability of an infinite number of photons. Several of our theoretical predictions are compared with predictions based on the Susskind-Glogower and the Pegg-Barnett operators, and they are also tested by experiment. We find that the experimental results confirm our theory in every case, and this includes tests of the higher moments of the measured cosine operator.