Photon Creation Research Articles

Measuring microwave quantum states: Tomogram and moments

Two measurable characteristics of microwave one-mode photon states are discussed: a rotated quadrature distribution (tomogram) and normally and antinormally ordered moments of photon creation and annihilation operators. Extraction of these characteristics from an amplified microwave signal is presented. Relations between the tomogram and the moments are found and can be used as a cross-check of experiments. Formalism of the ordered moments is developed. The state purity and generalized uncertainty relations are considered in terms of moments. Unitary and nonunitary time evolution of moments is obtained in the form of a system of linear differential equations in contrast to partial differential equations for quasidistributions. Time evolution is specified for the cases of a harmonic oscillator and a damped harmonic oscillator which describe noiseless and decoherence processes, respectively.

Creation of collective many-body states and single photons from two-dimensional Rydberg lattice gases

The creation of collective many-body quantum states from a two-dimensional lattice gas of atoms is studied. Our approach relies on the van der Waals interaction that is present between alkali metal atoms which are laser excited to high-lying Rydberg s-states. We focus on a regime in which the laser driving is strong compared to the interaction between Rydberg atoms. Here energetically low-lying many-particle states can be calculated approximately from a quadratic Hamiltonian. The potential usefulness of these states as a resource for the creation of deterministic single-photon sources is illustrated. The properties of these photon states are determined from the interplay between the particular geometry of the lattice and the interatomic spacing.

Nanoparticle toxicity and cancer

Nanoparticles (NPs) have provided significant advancements in cancer treatment. But as in any technology, there is a darkside. Experiments have shown NPs in body fluids pose a health risk by causing DNA damage that in of itself may lead to cancer. To avoid the dilemma that NPs are toxic to both cancer cells and DNA alike, the mechanism of NP toxicity must be understood so that the safe use of NPs may go forward. Reactive oxidative species (ROS) of peroxide and hydroxyl radicals damage the DNA by chemical reaction, but require NPs provide energies of about 5 eV not possible by surface effects. Only electromagnetic (EM) radiations beyond ultraviolet (UV) levels may explain the toxicity of NPs. Indeed, experiments show DNA damage from <100 nm NPs mimic the same reaction pathways of conventional sources of ionizing radiation, Hence, it is reasonable to hypothesize that NPs produce their own source of UV radiation, albeit at low intensity. Ionizing radiation from NPs at UV levels is consistent with the theory of QED induced EM radiation. QED stands for quantum electrodynamics. By this theory, fine < 100 nm NPs absorb low frequency thermal energy in the far infrared (FIR) from collisions with the water molecules in body fluids. Since quantum mechanics (QM) precludes NPs from having specific heat, absorbed EM collision energy cannot be conserved by an increase in temperature. But total internal reflection (TIR) momentarily confines the absorbed EM energy within the NP. Conservation proceeds by the creation of QED photons by frequency up-conversion of the absorbed EM energy to the TIR confinement frequency, typically beyond the UV. Subsequently, the QED photons upon scattering from atoms within the NP avoid TIR confinement and leak UV to the surroundings, thereby explaining the remarkable toxicity of NPs. But QED radiation need not be limited to natural or man-made NPs. Extensions suggest UV radiation is produced from biological NPs within the body, e.g., enzyme induced fragmentation of epithelial tissue, exocytosis of small proteins, and ironically, the same molecular markers used to detect cancer itself.

Controlled cavity-assisted generation of single and entangled photons in semiconductor quantum dots

We propose a scheme, based on a single semiconductor quantum dot inside a microcavity, for the creation of single and entangled photons with controllable waveform. A lateral electric field allows to charge the quantum dot with a single electron, and breaks the usual optical selection rules. Our scheme utilizes cavity-assisted stimulated Raman adiabatic passage (STIRAP) in order to promote the surplus electron from the ground to the excited state, via excitation of a pump pulse and optical coupling to the charged exciton. This transfer is accompanied by a synchronized emission of a single-photon wavepacket, whose waveform can be controlled by the pump pulse. We investigate the influence of phonon scatterings, and show that they allow to reset the single-photon source. Finally, we propose a slight variant of our scheme which would allow for the creation of entangled multi-photon states. All our simulations are performed with realistic quantum dot and cavity parameters, which allows us to argue that our scheme can be implemented with state-of-the-art quantum dots and microcavities.

Relaxation of Resonant Excitons in CdSe Nanocrystals: Simple Variational Calculation

The details of energy relaxation and multiple phonon scattering of a resonantly excited electron-hole pair confined in CdSe nanoparticle are studied at low temperature. Simple variational calculation of Ritz type have been performed to explain relaxation of excitons resonantly excited in CdSe nanoparticles in the case if initial photon absorption and creation of electron-hole pair takes place in the peripheral part of nanoparticle.

Photon creation in a resonant cavity with a nonstationary plasma mirror and its detection with Rydberg atoms

We investigate the dynamical Casimir effect and its detection with Rydberg atoms. The photons are created in a resonant cavity with a plasma mirror of a semiconductor slab which is irradiated by periodic laser pulses. The canonical Hamiltonian is derived for the creation and annihilation operators, showing the explicit time variation in the couplings, which originates from the external configuration such as a nonstationary plasma mirror. The number of created photons is evaluated as squeezing from the Heisenberg equations with the Hamiltonian. Then the detection of the photons as the atomic excitations is examined through the atom-field interaction. Some consideration is made for a feasible experimental realization with a semiconductor plasma mirror.

Engineered optical nonlinearity for quantum light sources

Many applications in optical quantum information processing benefit from careful spectral shaping of single-photon wave-packets. In this paper we tailor the joint spectral wave-function of photons created in parametric downconversion by engineering the nonlinearity profile of a poled crystal. We designed a crystal with an approximately Gaussian nonlinearity profile and confirmed successful wave-packet shaping by two-photon interference experiments. We numerically show how our method can be applied for attaining one of the currently most important goals of single-photon quantum optics, the creation of pure single photons without spectral correlations.

Collective photon emission from symmetric states created with Rydberg atoms on a ring lattice

We discuss the creation of non-classical light from collective atomic states that are prepared in a ring-shaped lattice. These states are realized by exploiting the strong interaction between atoms in high lying energy levels - so-called Rydberg states - and yield a resource for creating excitations of the electromagnetic field that carry few photons. We characterize the properties of these photonic states showing that they are determined by the interplay between the ring geometry, the structure of the atomic resource states and the collectivity in the photon emission which is controlled by the lattice spacing. The system permits the creation of single photons with well-defined orbital angular momentum and two-photon states that are entangled in orbital angular momentum.

Limits on decaying dark energy density models from the CMB temperature–redshift relation

The nature of the dark energy is still a mystery and several models have been proposed to explain it. Here we consider a phenomenological model for dark energy decay into photons and particles as proposed by Lima (J. Lima, Phys. Rev. D 54, 2571 (1996)). He studied the thermodynamic aspects of decaying dark energy models in particular in the case of a continuous photon creation and/or disruption. Following his approach, we derive a temperature redshift relation for the CMB which depends on the effective equation of state $w_{eff}$ and on the "adiabatic index" $\gamma$. Comparing our relation with the data on the CMB temperature as a function of the redshift obtained from Sunyaev-Zel'dovich observations and at higher redshift from quasar absorption line spectra, we find $w_{eff}=-0.97 \pm 0.034$, adopting for the adiabatic index $\gamma=4/3$, in good agreement with current estimates and still compatible with $w_{eff}=-1$, implying that the dark energy content being constant in time.

On the quantum space–time structure of light

AbstractWe extend the quantum theory of Time Refraction for a generic spatial and temporal modulation of the optical properties of a medium, such as a dielectric or a gravitational field. The derivation of the local Bogoliubov transformations relating the global electromagnetic modes (valid over the entire span of space and time) with the local modes (valid for the vicinity of each spatial and temporal position) is presented and used in the evaluation of vacuum photon creation by the optical modulations of the medium. We use this approach to relate and review the results of different quantum effects such as the dynamical Casimir effect, space and Time Refraction, the Unruh effect and radiation from superluminal non-accelerated optical boundaries.

The quantum open systems approach to the dynamical Casimir effect

We analyze the introduction of dissipative effects in the study of the dynamical Casimir effect. We consider a toy model for an electromagnetic cavity that contains a semiconducting thin shell, which is irradiated with short laser pulses in order to produce periodic oscillations of its conductivity. The coupling between the quantum field in the cavity and the microscopic degrees of freedom of the shell induces dissipation and noise in the dynamics of the field. We argue that the photon creation process should be described in terms of a damped oscillator with non-local dissipation and colored noise.

Unified quantum jump superoperator for optical fields from the weak- to the strong-coupling limit

We derive a generalized quantum jump superoperator that can be used in the quantum trajectory description of single photon detectors, light-emitting diodes (LEDs), and lasers. Our model describes an optical single-mode cavity field coupled to a reservoir through a two-state quantum system and includes three physical parameters: the coupling of the field to the two-state system, the coupling of the two-state system to the reservoir, and the cavity loss rate. In this setup, the two-state system can act as a photodetector or as an energy-adding mechanism. In the first case, we assume that the reservoir acts as a damping mechanism for an ideal cavity and derive reduced field operators describing the photon detection events. Our model coincides with the commonly known quantum trajectory based photon counting models at the weak- and strong-coupling limits and is, furthermore, also applicable between their validity regimes. In the second case, we assume that the reservoir injects energy into a lossy cavity through the two-state system. Again we derive the reduced field operators describing photon creation events into the lossy cavity. We show that this setup can act as an LED or as a laser depending on the strength of the injection. We also investigatemore » how the setup operates at the close proximity of the lasing threshold.« less

Cavity-QED based scheme for realization of photon annihilation and creation operations and their combinations

Theoretical analysis is given of an experimental scheme that can perform individual photon operations such as the photon annihilation operation a, creation operation a†, and commutation operation aa†−a†a, utilizing atom-cavity field interactions and conditional measurements. In order for the scheme to perform the desired photon operation, the atom-cavity field interaction times are generally required to be sufficiently short that photon annihilation and/or creation are dominated by the one-half Rabi cycle process. Such short interaction times, however, lead inevitably to a low success probability of the scheme. It is shown that this problem of low success probability can be overcome by preparing the cavity field in a superposition of a small number (two) of Fock states and choosing the interaction times appropriately.

Dynamical Casimir effect for TE and TM modes in a resonant cavity bisected by a plasma sheet

Parametric photon creation via the dynamical Casimir effect (DCE) is evaluated numerically, in a three-dimensional rectangular resonant cavity bisected by a semiconductor diaphragm (SD), which is irradiated by a pulsed laser with frequency of GHz order. The aim of this paper is to determine some of the optimum conditions required to detect DCE photons relevant to a novel experimental detection system. We expand upon the thin plasma sheet model [Crocce et al., Phys. Rev. A 70 033811 (2004)] to estimate the number of photons for both TE and TM modes at any given SD position. Numerical calculations are performed considering up to 51 inter-mode couplings by varying the SD location, driving period and laser power without any perturbations. It is found that the number of photons created for TE modes strongly depends on SD position, where the strongest enhancement occurs at the midpoint (not near the cavity wall); while TM modes have weak dependence on SD position. Another important finding is the fact that significant photon production for TM$_{111}$ modes still takes place at the midpoint even for a low laser power of 0.01 micro J/pulse, although the number of TE$_{111}$ photons decreases almost proportionately with laser power. We also find a relatively wide tuning range for both TE and TM modes that is correlated with the frequency variation of the instantaneous mode functions caused by the interaction between the cavity photons and conduction electrons in the SD excited by a pulsed laser.

Photon creation from vacuum and interactions engineering in nonstationary circuit QED

We study theoretically the nonstationary circuit QED system in which the artificial atom transition frequency, or the atom-cavity coupling, have a small periodic time modulation, prescribed externally. The system formed by the atom coupled to a single cavity mode is described by the Rabi Hamiltonian. We show that, in the dispersive regime, when the modulation periodicity is tuned to the 'resonances', the system dynamics presents the dynamical Casimir effect, resonant Jaynes-Cummings or resonant Anti-Jaynes-Cummings behaviors, and it can be described by the corresponding effective Hamiltonians. In the resonant atom-cavity regime and under the resonant modulation, the dynamics is similar to the one occurring for a stationary two-level atom in a vibrating cavity, and an entangled state with two photons can be created from vacuum. Moreover, we consider the situation in which the atom-cavity coupling, the atomic frequency, or both have a small non-periodic time modulation, and show that photons can be created from vacuum in the dispersive regime. Therefore, an analog of the dynamical Casimir effect can be simulated in circuit QED, and several photons, as well as entangled states, can be generated from vacuum due to the anti-rotating term in the Rabi Hamiltonian.

Fast Excitation and Photon Emission of a Single-Atom-Cavity System

We report on the fast excitation of a single atom coupled to an optical cavity using laser pulses that are much shorter than all other relevant processes. The cavity frequency constitutes a control parameter that allows the creation of single photons in a superposition of two tunable frequencies. Each photon emitted from the cavity thus exhibits a pronounced amplitude modulation determined by the oscillatory energy exchange between the atom and the cavity. Our technique constitutes a versatile tool for future quantum networking experiments.

Atomic vapor cells meet integrated optics

The demonstration of slow, fast, and stopped light1 has helped generate considerable interest in quantum interference effects. In addition to producing intriguing physical phenomena, these effects will be valuable for future optical communications. Buffers using slow-light modules will be important elements in alloptical data networks. Cryptography systems may also be expected to use quantum interference effects for photon creation and detection. But if slow-light buffers and quantum cryptography are to be practical in real-world applications, wemust create miniaturized, stand-alone quantum interference modules. This is the aim of research involving on-chip atomic vapor cells integrated with optical waveguides Slow-light effects are a product of a medium with large, frequency-dependent gain or absorption features that then give rise to large dispersion characteristics. Our work employs quantum interference effects in atomic vapor to create large dispersion. At present, atomic vapor can provide excellent dispersion characteristics, but it usually requires a large system footprint. In classical optical setups, which beam a laser through a transparent vapor cell, there is also a constant trade-off between focal depth and beamwidth. By using on-chip hollow-core optical antiresonant reflecting optical waveguides (ARROWs), we are able to direct light down vapor-filled cores, maintaining large optical intensities over long distances. This is particularly beneficial for nonlinear optical effects that can be exploited for single-photon generation and detection. In addition, ARROW-based platforms also require only a small footprint (1×1cm). ARROWs are constructed by growing alternating layers of silicon oxide and silicon nitride around a sacrificial core on a silicon wafer. The alternating dielectric materials with specific thicknesses confine and guide light through antiresonance. After etching out the sacrificial core, we are left with a hollow channel into which we can introduce various gases and liquids for optical experiments. Solid waveguides etched into the silicon on Figure 1. A rubidium (Rb)-loaded ARROW atomic vapor cell.

Probing Quantum Commutation Rules by Addition and Subtraction of Single Photons to/from a Light Field

The possibility of arbitrarily "adding" and "subtracting" single photons to and from a light field may give access to a complete engineering of quantum states and to fundamental quantum phenomena. We experimentally implemented simple alternated sequences of photon creation and annihilation on a thermal field and used quantum tomography to verify the peculiar character of the resulting light states. In particular, as the final states depend on the order in which the two actions are performed, we directly observed the noncommutativity of the creation and annihilation operators, one of the cardinal concepts of quantum mechanics, at the basis of the quantum behavior of light. These results represent a step toward the full quantum control of a field and may provide new resources for quantum information protocols.

Dynamical Casimir Effect in Braneworlds

In braneworld cosmology the expanding Universe is realized as a brane moving through a warped higher-dimensional spacetime. Like a moving mirror causes the creation of photons out of vacuum fluctuations, a moving brane leads to graviton production. We show that, very generically, Kaluza-Klein (KK) particles scale like stiff matter with the expansion of the Universe and can therefore not represent the dark matter in a warped braneworld. We present results for the production of massless and KK gravitons for bouncing branes in five-dimensional anti-de Sitter space. We find that for a realistic bounce the back reaction from the generated gravitons will be most likely relevant. This Letter summarizes the main results and conclusions from numerical simulations which are presented in detail in a long paper [M. Ruser and R. Durrer, arXiv:0704.0790].

Competition between excitons and exciplexes: Experiments on multilayered organic light emitting diodes

The electronic processes responsible for charge transport and electroluminescence in multilayered organic light emitting diodes (OLEDs) are very sensitive to the properties of the organic heterojunction. In particular, the height of the energy barrier affects the way in which electrons and holes meet at the heterojunction, the way in which the barrier is crossed, and the probability for photon creation. We investigate these aspects experimentally using a family of OLED devices in which different hole transporting materials are used in otherwise identical device architectures to vary the interfacial hole barrier over a wide energy range. We find that the quantum efficiency of the device is maximum for low-energy barriers and drops for high barrier values where a redshifted electroluminescence spectrum is observed. This shift is attributed to exciplex generation at the heterojunction. The contributions of exciton and exciplex annihilation in radiative and nonradiative channels to the charge flow within the heterojunction region are separated and quantified.