We study quantum intensity correlations produced using four-wave mixing in a room-temperature rubidium
vapor cell. An extensive study of the effect of the various parameters allows us to observe very large amounts of
non classical correlations.
In the last years we have proposed the use of the mechanism of spontaneous symmetry breaking with the purpose of
generating perfect quadrature squeezing. Here we review previous work dealing with spatial (translational and rotational)
symmetries, both on optical parametric oscillators and four-wave mixing cavities, as well as present new results. We then
extend the phenomenon to the polarization state of the signal field, hence introducing spontaneous polarization symmetry
breaking. Finally we propose a Jaynes-Cummings model in which the phenomenon can be investigated at the singlephoton-
pair level in a non-dissipative case, with the purpose of understanding it from a most fundamental point of view.
The coupling of mechanical oscillators with light has seen a recent surge of interest, as recent reviews report. 1,2 This
coupling is enhanced when confining light in an optical cavity where the mechanical oscillator is integrated as backmirror
or movable wall. At the nano-scale, the optomechanical coupling increases further thanks to a smaller
optomechanical interaction volume and reduced mass of the mechanical oscillator. In view of realizing such cavity nanooptomechanics
experiments, a scheme was proposed where a sub-wavelength sized nanomechanical oscillator is coupled
to a high finesse optical microcavity. 3 Here we present such an experiment involving a single nanomechanical rod
precisely positioned into the confined mode of a miniature Fabry-Pérot cavity. 4 We describe the employed stabilized
cavity set-up and related finesse measurements. We proceed characterizing the nanorod vibration properties using
ultrasonic piezo-actuation methods. Using the optical cavity as a transducer of nanomechanical motion, we monitor
optically the piezo-driven nanorod vibration. On top of extending cavity quantum electrodynamics concepts to
nanomechanical systems, cavity nano-optomechanics should advance into precision displacement measurements near the
standard quantum limit 5 , investigation of mechanical systems in their quantum regime, non-linear dynamics 6 and sensing
Different adiabatic passage methods are applied as part of a state mapping scheme in multilevel trapped systems.
The aim is to achieve full population transfer from the rotational states of a trapped molecular ion to its
translational states. Our analysis is based on numerical simulations with the master equation. We discuss how
the resolved sideband condition, and spontaneous emission have an adverse effect on the efficiency for stimulated
Raman adiabatic passage. Use of adiabatic rapid passage techniques, with two-photon Raman transitions results
in higher efficiencies that can exceed 97%.
A new developed for storing quantum information on atomic polaritons being at thermal equilibrium is developed
for the first time. We propose a new type of spatially periodic structure - polaritonic crystal (PolC) formed
by trapped two-level atoms interacting with quantum electromagnetic field in one-dimensional array of tunnelcoupled
microcavities, which allows polaritons to be fully localized. The quantum degeneracy and phase transition
to superfluid (Bardeen-Cooper-Schrieffer-type) state for low branch polaritons is discussed. The principal result is
that the group velocity of polaritons depends essentially on the order parameter of the system, i.e. on the average
photon number in the cavity array. An algorithm for the spatially distributed writing, storing, and retrieving of
quantum optical information using polariton wave packet propagated in the cavity array is examined. To take
into account decoherence processes in polaritonic system the quantum Brownian particle model is discussed as
A novel method of multi-bit quantum optical data storage is presented, where the storage time can be lengthened far
beyond the spin phase-decay time in a reversible spin inhomogeneous system excited by consecutive resonant
Raman optical data pulses. The ultralong storage time is obtained by an optical population locking mechanism of
modified rephasing process. This gives potentials to quantum repeaters utilizing quantum memories for long
distance quantum communications, in which ultralong storage time plays a major role.
Few-photon systems are best described by their wave function rather than by the usual quantum field formalism.
In this work, we develop a photon wave function (PWF) formalism suitable for analyzing a wide variety of
quantum optical problems related to propagation, diffraction and imaging with quantum states of light. We
establish a generalized Huygens-Fresnel (GH-F) principle that describes the propagation of any paraxial N-photon
state. This tool is very helpful for predicting photo-detection correlations in space and time due to an
initial N-particle entanglement, even in complex situation. The effect of lenses, beam splitters, filters ... on the
photon paths can be easily taken into account. We apply the PWF formalism and the GH-F principle to three
specific problems in quantum optics. First, we revisit the Hong-Ou-Mandel two-photon interference effect and
analyze the effect of photon shape mismatch in space, time and polarization using the PWF formalism. Second,
we show how to use the GH-F principle to analyze "ghost" imaging and diffraction experiments with entangled
photon pairs such as those realized by Strekalov et al. [Phys. Rev. Lett. 74, 3600 (1995)] and Pittman et al.
[Phys. Rev. A 52, R3429 (1995)] in the nineties. Finally, we use the GH-F principle to analyze the resolution
enhancement in a recent quantum imaging proposal based on N incoherent single-photon sources [Phys. Rev.
Lett. 99, 133603 (2007) and Phys. Rev. A 80, 013820 (2009)].
We propose the use of modal engineered tapered optical fibers for single photon interferometry experiments.
Tapered optical fibers (TOF) can be designed to function as tunable Mach-Zehnder (MZ) type modal single photon
interferometer. The MZ design criteria of tunability, visibility, and wavelength range are inherently interconnected in
TOF's, which makes the design complex. Moreover, novel TOF related design criteria, like loss minimization, have to be
taken into account. Design guidelines can be based on a semi-analytical approach assuming multiple two mode beat
equations for different mode power amplitudes. Linearization permits to obtain a set of simple and robust analytical
relations that correlate the TOF design parameter with the TOF and MZI optical properties.
By focusing on the tunability, we have demonstrated a device that permits to be tuned between local minima and
The results of frequency-modulation (FM) spectroscopy of coherent dark resonances from the Zeeman sublevels
of the transition F=2 ↔ F=1 of D1 line in absorption of 87Rb atoms are presented and discussed in detail.
By contrast with the conventional spectroscopy of coherent dark resonances employing two laser beams, relative
frequency of which can be varied, these data has been obtained with the help of a single frequency-modulated
laser field. Variation of the modulation frequency plays then similar role with variation the relative frequency
in conventional spectroscopy. Experimental data are fit to the theoretical calculations, which are based on
the theory of FM spectroscopy of coherent dark resonances recently developed by us. Feasibility of using such
experimental technique for accurate measurements of magnetic fields is also discussed.
In the space of mixed states the Schrödinger-Robertson uncertainty relation holds though it can never be saturated.
Two tight extensions of this relation in the space of mixed states exist; one proposed by Dodonov
and Man'ko, where the lower limit on the uncertainty depends on the purity of the state, and another where
the uncertainty is bounded by the von Neumann entropy of the state proposed by Bastiaans. Driven by the
needs that have emerged in the field of quantum information, in a recent work we have extended the puritybounded
uncertainty relation by adding an additional parameter characterizing the state, namely its degree of
non-Gaussianity. In this work we alternatively present a extension of the entropy-bounded uncertainty relation.
The common points and differences between the two extensions of the uncertainty relation help us to draw more
general conclusions concerning the bounds on the non-Gaussianity of mixed states.
Quantum multipartite entanglement is a striking phenomenon predicted by quantum mechanics when several
parts of a physical system share the same quantum state that cannot be factorized into the states of individual
subsystems. The Gaussian quantum states are usually characterized by the covariance matrix of the quadrature
components. A powerful formalism for treating the Gaussian states is that of the symplectic eigenvalues. In
particular, a quantitative measure of multipartite entanglement is the so-called logarithmic negativity, related
to the symplectic eigenvalues of the partially transposed covariance matrix.
Considering only global variances of the field quadratures one completely neglects the spatiotemporal properties
of the electromagnetic field. We propose, following the spirit of quantum imaging, to generalize the theory
of multipartite entanglement for the continuous variable Gaussian states by considering the local correlation
matrix at two different spatiotemporal points [see manuscript for characters] and [see manuscript for characters] with [see manuscript for characters] being the transverse coordinate. For
stationary and homogeneous systems one can also introduce the spatiotemporal Fourier components of the correlation
matrix. The formalism of the global symplectic eigenvalues can be straightforwardly generalized to
the frequency-dependent symplectic eigenvalues. This generalized theory allows, in particular, to introduce the
characteristic spatial area and time of the multipartite entanglement, which in general depend on the number of
"parties" in the system.
As an example we consider multipartite entanglement in spontaneous parametric down-conversion with
spatially-structured pump. We investigate spatial properties of such entanglement and calculate its characteristic
We study the transmission of classical information via optical Gaussian channels with a classical additive noise
under the physical assumption of a finite input energy including the energy of classical signal (modulation)
and the energy spent on squeezing the quantum states carrying information. Multiple uses of a certain class of
memory channels with correlated noise is equivalent to one use of parallel independent channels generally with
a phase-dependent noise. The calculation of the channels capacity implies finding the optimal distribution of
the input energy between the channels. Above a certain input energy threshold, the optimal energy distribution
is given by a solution known in the case of classical channels as water-filling. Below the threshold, the optimal
distribution of the input energy depends on the noise spectrum and on the input energy level, so that the channels
fall into three different classes: the first class corresponds to very noisy channels excluded from information
transmission, the second class is composed of channels in which only one quadrature (q or p) is modulated
and the third class corresponds to the water-filling solution. Although the non-modulated quadrature in the
channels of the second class is not used for information transmission, a part of the input energy is used for the
squeezing the quantum state which is a purely quantum effect. We present a complete solution to this problem
for one mode and analyze the influence of the noise phase dependence on the capacity. Contrary to our intuition,
in the highly phase-dependent noise limit, there exists a universal value of the capacity which neither depends
on the input energy nor on the value of noise temperature. In addition, similarly to the case of lossy channels
for weak thermal contribution of the noise, there exists an optimal squeezing of the noise, which maximizes the
The radar cross section σC is an objective measure of the "radar visibility" of an object. As such, σC is an important concept for the correct characterization of the operational performance of radar systems. Furthermore,
σC is equally essential for the design and development of stealth weapon systems and platforms. Recent years
have seen the theoretical development of quantum radars, that is, radars that operate with a small number
of photons. In this regime, the radar-target interaction is described through photon-atom scattering processes
governed by the laws of quantum electrodynamics. As such, it is theoretically inconsistent to use the same σC
to characterize the performance of a quantum radar. In this paper we define a quantum radar cross section σQ
based on quantum electrodynamics and interferometric considerations. We discuss the theoretical challenges of
defining σQ, as well as computer simulations of σC and σQ for simple targets.
Photon sources for multi-photon entanglement experiments are commonly based on the process of spontaneous
parametric down conversion. Due to the probabilistic photon production, such experiments suffer from low multiphoton
count rates. To increase this count rate, we present a novel SPDC pump source based on a femtosecond
UV enhancement cavity that increases the available pump power while maintaining a high repetition rate of
80MHz. We apply the cavity as photon source for realizing symmetric, multi-partite entangled Dicke states,
which are observed with a high rate and high fidelity. We characterize the observed Dicke states of up to six
photons using efficient tools exploiting the state's symmetries.
We demonstrate an integrated semiconductor ridge microcavity source of counterpropagating twin photons at room
temperature in the telecom range. Based on type II parametric down conversion in a counterpropagating phase matching
scheme with transverse pump, the device generates around 10-11 pairs/pump photons having a 0.3 nm bandwidth for a 1
mm long waveguide. The emission spectrum shows the existence of two equally probable processes, which is a
preliminary step to the direct generation of Bell states. The twin character of the photons of each pair is demonstrated via
a temporal correlation measurement. These results open the way to the demonstration of several interesting features
associated to the counterpropagating geometry, such as the control of the frequency correlation degree via the spatial and
spectral properties of the pump beam.
We demonstrate electrically pumped single-photon emission in the visible spectral range from InP quantum dots
embedded in a resonant cavity LED device structure. The electroluminescence from a single QD can be observed
up to 120 K. Our devices can also be operated using pulsed electrical excitation. The successful injection of
carriers is verified by time-correlated photon counting experiments and the pulsed signature in second-order
Color centers in diamond are very promising candidates among the possible realizations for practical singlephoton
sources because of their long-time stable emission at room temperature. The popular nitrogen-vacancy
center shows single-photon emission, but within a large, phonon-broadened spectrum (≈ 100 nm), which strongly
limits its applicability for quantum communication. By contrast, Ni-related centers exhibit narrow emission lines
at room temperature. We present investigations on single color centers consisting of Ni and Si created by ion
implantation into single crystalline IIa diamond. We use systematic variations of ion doses between 108 cm-2 and
1014 cm-2 and energies between 30 keV and 1.8MeV. The Ni-related centers show emission in the near infrared
spectral range (≈ 770 nm to 787 nm) with a small line-width (≈ 3 nm FWHM). A measurement of the intensity
correlation function proves single-photon emission. Saturation measurements yield a rather high saturation count
rate of 77.9kcounts/s. Polarization dependent measurements indicate the presence of two orthogonal dipoles.
The dual nature of photons is well known but in spite of several years of work its foundation is not well understood. In
the present paper, a fresh approach is proposed according to which fields and particles are transformed into each other
and propagate together. This is explained by considering the field quantization process with the help of annihilation and
creation operators. Thus, at every point in space and time the sum of the energies associated with electric, magnetic
fields and photons is conserved. The present investigation supports the recently observed experimental data related with
sub wavelength interference and its regain by detecting photons with the help of the photon-echo process.
This paper reports on trapping and laser-cooling of singly-ionized strontium ions in a linear Paul trap. We
demonstrate loading of large ion clouds containing as much as 106 ions and laser cooling down to the Coulomb
crystal transition. We observe the spatial segregation of the different Sr+ isotopes due to the mass-dependent
Paul trap stiffness. Sympathetic cooling of the different isotopes is demonstrated, either by laser-cooling of 88Sr+
(83% abundance) or of 86Sr+ (10% abundance). These demonstrations open the way to the use of a large ion
Coulomb crystal for quantum optics and quantum information experiments, where the strong confinement, the
long lifetime, and the absence of perturbation by cooling lasers are crucial.
Single cesium atom prepared in a large-magnetic-gradient magneto-optical trap (MOT) has been efficiently loaded into a
microscopic far-off-resonance optical trap (FORT, or optical tweezer), and the atom can be transferred back and forth
between two traps with high efficiency. The intensity noise spectra of tweezer laser are measured and the heating
mechanisms in optical tweezer are analyzed. To prolong the lifetime of single atom trapped in optical tweezer, laser
cooling technique is utilized to decrease atom's kinetic energy, and the effective temperature of single atom in tweezer is
estimated by the release-and-recapture (R&R) method. Thanks to laser cooling, typical lifetime of ~ 130.6 ± 1.8 s for
single atom in tweezer is obtained. These works provides a good starting point for coherent manipulation of single atom.