Experimental determination of a nonclassical Glauber-Sudarshan P function

A quantum state is nonclassical if its Glauber-Sudarshan P function fails to be interpreted as a probability density. This quantity is often highly singular, so that its reconstruction is a demanding task. Here we present the experimental determination of a well-behaved P function showing negativities for a single-photon-added thermal state. This is a direct visualization of the original definition of nonclassicality. The method can be useful under conditions for which many other signatures of nonclassicality would not persist.Comment: 4 pages, 4 figure

Nonclassical Moments and their Measurement

Practically applicable criteria for the nonclassicality of quantum states are formulated in terms of different types of moments. For this purpose the moments of the creation and annihilation operators, of two quadratures, and of a quadrature and the photon number operator turn out to be useful. It is shown that all the required moments can be determined by homodyne correlation measurements. An example of a nonclassical effect that is easily characterized by our methods is amplitude-squared squeezing.Comment: 12 pages, 6 figure

Convex ordering and quantification of quantumness

The characterization of physical systems requires a comprehensive understanding of quantum effects. One aspect is a proper quantification of the strength of such quantum phenomena. Here, a general convex ordering of quantum states will be introduced which is based on the algebraic definition of classical states. This definition resolves the ambiguity of the quantumness quantification using topological distance measures. Classical operations on quantum states will be considered to further generalize the ordering prescription. Our technique can be used for a natural and unambiguous quantification of general quantum properties whose classical reference has a convex structure. We apply this method to typical scenarios in quantum optics and quantum information theory to study measures which are based on the fundamental quantum superposition principle.Comment: 9 pages, 2 figures, revised version; published in special issue "150 years of Margarita and Vladimir Man'ko

Detection of quantum light in the presence of noise

Detection of quantum light in the presence of dark counts and background radiation noise is considered. The corresponding positive operator-valued measure is obtained and photocounts statistics of quantum light in the presence of noise is studied.Comment: 4 pages, 1 figure; misprints correcte

Spontaneous decay of excited atomic states near a carbon nanotube

Spontaneous decay process of an excited atom placed inside or outside (near the surface) a carbon nanotube is analyzed. Calculations have been performed for various achiral nanotubes. The effect of the nanotube surface has been demonstrated to dramatically increase the atomic spontaneous decay rate -- by 6 to 7 orders of magnitude compared with that of the same atom in vacuum. Such an increase is associated with the nonradiative decay via surface excitations in the nanotube.Comment: 8 pages, 3 figure

Spontaneous decay of an emitter's excited state near a finite-length metallic carbon nanotube

The spontaneous decay of an excited state of an emitter placed in the vicinity of a metallic single-wall carbon nanotube (SWNT) was examined theoretically. The emitter-SWNT coupling strongly depends on the position of the emitter relative to the SWNT, the length of the SWNT, the dipole transition frequency and the orientation of the emitter. In the high-frequency regime, dips in the spectrum of the spontaneous decay rate exist at the resonance frequencies in the spectrum of the SWNT conductivity. In the intermediate-frequency regime, the SWNT conductivity is very low, and the spontaneous decay rate is practically unaffected by the SWNT. In the low-frequency regime, the spectrum of the spontaneous decay rate contains resonances at the antennas resonance frequencies for surface-wave propagation in the SWNT. Enhancement of both the total and radiative spontaneous decay rates by several orders in magnitude is predicted at these resonance frequencies. The strong emitter-field coupling is achieved, in spite of the low Q factor of the antenna resonances, due to the very high magnitude of the electromagnetic field in the near-field zone. The vacuum Rabi oscillations of the population of the excited emitter state are exhibited when the emitter is coupled to an antenna resonance of the SWNT.Comment: 8 pages, 6 figure

Tailoring and enhancing spontaneous two-photon emission processes using resonant plasmonic nanostructures

The rate of spontaneous emission is known to depend on the environment of a light source, and the enhancement of one-photon emission in a resonant cavity is known as the Purcell effect. Here we develop a theory of spontaneous two-photon emission for a general electromagnetic environment including inhomogeneous dispersive and absorptive media. This theory is used to evaluate the two-photon Purcell enhancement in the vicinity of metallic nanoparticles and it is demonstrated that the surface plasmon resonances supported by these particles can enhance the emission rate by more than two orders of magnitude. The control over two-photon Purcell enhancement given by tailored nanostructured environments could provide an emitter with any desired spectral response and may serve as an ultimate route for designing light sources with novel properties

Generation of Squeezed States of Nanomechanical Resonators by Reservoir Engineering

An experimental demonstration of a non-classical state of a nanomechanical resonator is still an outstanding task. In this paper we show how the resonator can be cooled and driven into a squeezed state by a bichromatic microwave coupling to a charge qubit. The stationary oscillator state exhibits a reduced noise in one of the quadrature components by a factor of 0.5 - 0.2. These values are obtained for a 100 MHz resonator with a Q-value of 10$^4$ to 10$^5$ and for support temperatures of T $\approx$ 25 mK. We show that the coupling to the charge qubit can also be used to detect the squeezed state via measurements of the excited state population. Furthermore, by extending this measurement procedure a complete quantum state tomography of the resonator state can be performed. This provides a universal tool to detect a large variety of different states and to prove the quantum nature of a nanomechanical oscillator.Comment: 13 pages,9 figure

Quantum state engineering

We show how to create an arbitrary field state in a cavity by sending appropriately prepared two-level atoms through the cavity and subsequently detecting them in their ground state