Large Number Of Photons Research Articles

Heating of Intergalactic Gas Near Growing Black Holes During the Hydrogen Reionization Epoch

Black holes growing during Eddington accretion emit a large number of ultraviolet and x-ray photons which can influence the ionization and thermal state of the surrounding intergalactic gas before the onset of the hydrogen reionization epoch in the universe. This radiation heats the gas beyond the temperature of the relict radiation (cosmic microwave background CMB) TCMB (z) to a red shift z ~ 8 –12 within 0.1-3 Mpc of a black hole with initial mass ~300 M⨀ formed at z ~ 20-50 and growing with radiation efficiency e ~ 0.15 – 0.075. The size of the gas regions in which the degree of ionization of hydrogen is higher than the residual value after recombination, i.e., greater than 10-4, approaches the same levels. More substantial heating and ionization of the gas takes place in a smaller volume. In the vicinity of 30-300 kpc, for the same black hole parameters, it is heated to above 104 K or almost an order of magnitude greater than around a black hole with almost constant mass. The radiative flux from growing black holes is sufficient for complete (above 99%) production of ionized hydrogen and doubly ionized helium within 3-10 kpc of the parent minihalo. The recombination time for hydrogen in the ionization zones surrounding the black holes exceeds the local age of the universe for z ≲ 10. These zones, which occupy several kiloparsecs, can become seeds for the next reionization of the universe. It turns out that extended regions with sizes of hundreds of kiloparsecs where radiation from growing black holes substantially changes the evolution of the intergalactic gas will radiate in the 21 cm line of atomic hydrogen, since the gas in these zones essentially remains neutral at a temperature exceeding that of the CMB.

Controllable generation of photons and phonons in a coupled Bose–Einstein condensate-optomechanical cavity via the parametric dynamical Casimir effect

We theoretically propose and investigate a feasible experimental scheme for the realization of the dynamical Casimir effect (DCE) in a hybrid optomechanical cavity with a moving end mirror containing an interacting cigar-shaped Bose–Einstein condensate (BEC). We show that in the red-detuned regime of cavity optomechanics together with the weak optomechanical coupling limit by coherent modulation of the s-wave scattering frequency of the BEC and the mechanical spring coefficient of the mechanical oscillator (MO), the mechanical and atomic quantum vacuum fluctuations are parametrically amplified, which consequently lead to the generation of the mechanical/Bogoliubov-type Casimir phonons. Interestingly, in the coherent regime corresponding to the case of largely different optomechanical coupling strengths of the cavity field to the BEC and the MO, or equivalently largely different cooperativities, one can generate a large number of Casimir photons due to the amplification of the intracavity vacuum fluctuations induced by the time modulations of the BEC and the MO. The number of generated Casimir particles are externally controllable by the cooperativities, and the modulation amplitudes of the atomic collisions rate and the mechanical spring coefficient.

A theoretical study on achieving the generalized binomial states with second harmonic generation processes

In this paper, the generalized binomial states (GBSs) are theoretical presented with second-harmonic generation (SHG) processes by utilizing the Schwinger–Bose operation realization. The GBSs are theoretically demonstrate by a combination of two fundamental-frequency light fields, which are incident upon a second-order nonlinear crystal under the type-II SHG configuration. One incident field is in the number state $$\left| M \right\rangle$$ , and the other is in coherent state of sufficiently strong intensity to be treated as a classical field. It is found that GBSs will eventually convert to the coherent states when the incident number-state field possess sufficiently large number of photons. The presented study provides an alternative and theoretically intriguing scheme to achieve the important GBSs.

Compact gain-saturated x-ray lasers down to 685 nm and amplification down to 585 nm

Plasma-based x-ray lasers allow single-shot nano-scale imaging and other experiments requiring a large number of photons per pulse to be conducted in compact facilities. However, compact repetitively fired gain-saturated x-ray lasers have been limited to wavelengths above λ=8.85 nm. Here we extend their range to λ=6.85 nm by transient traveling wave excitation of Ni-like Gd ions in a plasma created with an optimized pre-pulse followed by rapid heating with an intense sub-picosecond pump pulse. Isoelectronic scaling also produced strong lasing at 6.67 nm and 6.11 nm in Ni-like Tb and amplification at 6.41 nm and 5.85 nm in Ni-like Dy. This scaling to shorter wavelengths was obtained by progressively increasing the pump pulse grazing incidence angle to access increased plasma densities. We experimentally demonstrate that the optimum grazing incidence angle increases linearly with atomic number from 17 deg for Z=42 (Mo) to 43 deg for Z=66 (Dy). The results will enable applications of sub-7 nm lasers at compact facilities.

Optomechanically Induced Transparency and Cooling in Thermally Stable Diamond Microcavities

Diamond cavity optomechanical devices hold great promise for quantum technology based on coherent coupling between photons, phonons, and spins. These devices benefit from the exceptional physical properties of diamond, including its low mechanical dissipation and optical absorption. However, the nanoscale dimensions and mechanical isolation of these devices can make them susceptible to thermo-optic instability when operating at the high intracavity field strengths needed to realize coherent photon–phonon coupling. In this work, we overcome these effects through engineering of the device geometry, enabling operation with large photon numbers in a previously thermally unstable regime of red-detuning. We demonstrate optomechanically induced transparency with cooperativity >1 and normal mode cooling from 300 to 60 K and predict that these devices will enable coherent optomechanical manipulation of diamond spin systems.

Simulating quantum light propagation through atomic ensembles using matrix product states

A powerful method to interface quantum light with matter is to propagate the light through an ensemble of atoms. Recently, a number of such interfaces have emerged, most prominently Rydberg ensembles, that enable strong nonlinear interactions between propagating photons. A largely open problem is whether these systems produce exotic many-body states of light and developing new tools to study propagation in the large photon number limit is highly desirable. Here we provide a method based on a “spin model” that maps quasi one-dimensional (1D) light propagation to the dynamics of an open 1D interacting spin system, where all photon correlations are obtained from those of the spins. The spin dynamics in turn are numerically solved using the toolbox of matrix product states. We apply this formalism to investigate vacuum induced transparency, wherein the different photon number components of a pulse propagate with number-dependent group velocity and separate at output.

Scalable symmetry detector and its applications by using beam splitters and weak nonlinearities

We describe a method to detect twin-beam multiphoton entanglement based on a beam splitter and weak nonlinearities. For the twin-beam four-photon entanglement, we explore a symmetry detector. It works not only for collecting two-pair entangled states directly from the spontaneous parametric down-conversion process, but also for generating them by cascading these symmetry detectors. Surprisingly, by calculating the iterative coefficient and the success probability we show that with a few iterations the desired two-pair can be obtained from a class of four-photon entangled states. We then generalize the symmetry detector to n-pair emissions and show that it is capable of determining the number of the pairs emitted indistinguishably from the spontaneous parametric down-conversion source, which may contribute to explore multipair entanglement with a large number of photons.

Evaluation of clustering algorithms at the < 1 GeV energy scale for the electromagnetic calorimeter of the PADME experiment

A possible solution to the Dark Matter problem postulates that it interacts with Standard Model particles through a new force mediated by a “portal”. If the new force has a U(1) gauge structure, the “portal” is a massive photon-like vector particle, called dark photon or A’. The PADME experiment at the DAΦNE Beam-Test Facility (BTF) in Frascati is designed to detect dark photons produced in positron on fixed target annihilations decaying to dark matter (e+e-→γA′) by measuring the final state missing mass. One of the key roles of the experiment will be played by the electromagnetic calorimeter, which will be used to measure the properties of the final state recoil γ. The calorimeter will be composed by 616 21×21×230 mm3 BGO crystals oriented with the long axis parallel to the beam direction and disposed in a roughly circular shape with a central hole to avoid the pile up due to the large number of low angle Bremsstrahlung photons. The total energy and position of the electromagnetic shower generated by a photon impacting on the calorimeter can be reconstructed by collecting the energy deposits in the cluster of crystals interested by the shower. In PADME we are testing two different clustering algorithms, PADME-Radius and PADME-Island, based on two complementary strategies. In this paper we will describe the two algorithms, with the respective implementations, and report on the results obtained with them at the PADME energy scale (< 1 GeV), both with a GEANT4 based simulation and with an existing 5×5 matrix of BGO crystals tested at the DAΦNE BTF.

Quantum dynamics of a Josephson junction driven cavity mode system in the presence of voltage bias noise

We give a semiclassical analysis of the average photon number as well as photon number variance (Fano factor $F$) for a Josephson-junction (JJ) embedded microwave cavity system, where the JJ is subject to a fluctuating (i.e. noisy) bias voltage with finite dc average. Through the ac Josephson effect, the dc voltage bias drives the effectively nonlinear microwave cavity mode into an amplitude squeezed state ($F<1$), as has been established previously [A. D. Armour, et al., Phys. Rev. Lett. 111, 247001 (2013)], but bias noise acts to degrade this squeezing. We find that the sensitivity of the Fano factor to bias voltage noise depends qualitatively on which stable fixed point regime the system is in for the corresponding classical nonlinear steady state dynamics. Furthermore, we show that the impact of voltage bias noise is most significant when the cavity is excited to states with large average photon number.

Verifying cross-Kerr induced number squeezing: a case study

We analyse an experimental method for creating interesting nonclassical states by processing the entanglement generated when two large coherent states interact in a cross-Kerr medium. We specifically investigate the effects of loss and noise in every mode of the experiment, as well as the effect of ‘binning’ the post-selection outcomes. Even with these imperfections, we find an optimal set of currently achievable parameters which would allow a proof-of-principle demonstration of number squeezing in states with large mean photon number. We discuss other useful states which can be generated with the same experimental tools, including a class of states which contain coherent superpositions of differing photon numbers, e.g. good approximations to the state . Finally, we suggest one possible application of this state in the field of optomechanics.

Optimal lossy quantum interferometry in phase space

We analyse the phase space representation of the optimal measurement of a phase shift in an interferometer with equal photon loss in both its arms. In the local phase estimation scenario with a fixed number of photons, we identify features of the spin Wigner function that warrant sub-shot-noise precision, and discuss their sensitivity to losses. We derive the asymptotic form of an integral kernel describing the process of photon loss in the phase space in the limit of large photon numbers. The analytic form of this kernel allows one to assess the ultimate precision limit for a lossy interferometer. We also provide a general lower bound on the quantum Fisher information in terms of spin Wigner functions.

PawFLIM: reducing bias and uncertainty to enable lower photon count in FLIM experiments

Förster resonant energy transfer measured by fluorescence lifetime imaging microscopy (FRET-FLIM) is the method of choice for monitoring the spatio-temporal dynamics of protein interactions in living cells. To obtain an accurate estimate of the molecular fraction of interacting proteins requires a large number of photons, which usually precludes the observation of a fast process, particularly with time correlated single photon counting (TCSPC) based FLIM. In this work, we propose a novel method named pawFLIM (phasor analysis via wavelets) that allows the denoising of FLIM datasets by adaptively and selectively adjusting the desired compromise between spatial and molecular resolution. The method operates by applying a weighted translational-invariant Haar-wavelet transform denoising algorithm to phasor images. This results in significantly less bias and mean square error than other existing methods. We also present a new lifetime estimator (named normal lifetime) with a smaller mean squared error and overall bias as compared to frequency domain phase and modulation lifetimes. Overall, we present an approach that will enable the observation of the dynamics of biological processes at the molecular level with better temporal and spatial resolution.

Monte Carlo Basics for Radiation Dose Assessment in Diagnostic Radiology

Monte Carlo simulations are the basis of all modern x-ray dosimetry methods in diagnostic radiology. Monte Carlo (MC) methods are different from the larger class of computer simulation techniques in that they explicitly compute stochastic events and track the outcome. For x-ray dosimetry, MC methods track the trajectory of individual x-ray photons, one by one, as they exit an x-ray source, enter the simulated patient anatomy, and undergo scattering and absorption events. The amount of energy deposited in the “patient” is tallied at each location where a dose-deposition interaction takes place. Typically, millions to billions of photon histories are computed and the energy deposited in each volume element (voxel) in the mathematical phantom is then divided by the tissue mass of that voxel, resulting in the absorbed dose for the voxel – defined as imparted energy per unit mass. Modern computers are very fast and billions of photon histories can be realistically simulated to estimate the radiation dose deposited to anatomy from a given radiological imaging application. Despite this large number of simulated photons (e.g. 109), actual x-ray imaging involves 1014 to 1016 photons for each mammographic or CT acquisition, respectively – a factor of 10,000 or more greater than what is possible in most MC experiments. Thus, it is common to also record the air kerma at the entrance of the phantom for radiographic or mammographic applications, or the air kerma at the center of the field for computed tomography applications. In this way, a coefficient representing the absorbed dose per unit air kerma – in the interesting units of mGy/mGy, is computed. In the old days of radiology, these coefficients used different units and were sometimes called the “roentgen to rad conversion factors”. These coefficients allow dose levels in actual imaging procedures to be estimated using physically-measured air kerma levels in the radiography room or CT suite.

Coherent coupling between an optomechanical membrane and an interacting photon Bose–Einstein condensate

In this paper, we study theoretically the optomechanical interaction of an interacting condensate of photons with an oscillating mechanical membrane in a microcavity. We show that in the Bogoliubov approximation, due to the large number of photons in the condensate, there is a linear strong effective coupling between the Bogoliubov mode of the photonic Bose–Einstein condensate (BEC) and the mechanical motion of the membrane which depends on the photon–photon scattering potential. This coupling leads to the cooling of the mechanical motion, the normal mode splitting (NMS), the squeezing of the output field and the entanglement between the excited mode of the cavity and the mechanical mode. Since the photon condensation occurs at room temperature, this hybrid system can be potentially considered as a room temperature source of squeezed light as well as a suited candidate for exploring the quantum effects. We show that, on one hand, the non-linearity of the photon gas increases the degree of the squeezing of the output field of the microcavity and the efficiency of the cooling process at high temperatures. On the other hand, it reduces the NMS in the displacement spectrum of the oscillating membrane and the degree of the optomechanical entanglement. In addition, the temperature of the photonic BEC can be used to control the above-mentioned phenomena.

Unconventional photon blockade in a photonic molecule containing a quantum dot

We propose a scheme to realize strong photon antibunching with lower photon nonlinearity in a photonic molecule consisting of two photonic cavities, one of which contains a quantum dot (QD). This strong photon antibunching is attributed to destructive quantum interference effect which suppresses the two-photon excitation of the cavity field. That g2(0)≈10−4 can be achieved with modest QD-cavity coupling strength g=1.1κ and cavity tunneling strength J=3κ when the system is driven by single laser field. To further reduce the requisite tunneling and make the system tunable, two laser fields are applied to the system. The strong photon antibunching (g2(0)≈10−3) can be achieved with a relatively large intracavity photon number by optimizing the phase between two driving laser fields when J=0.9κ. Moreover, the system shows a strong robustness of maintaining strong photon antibunching within a large parameter variation under the optimal phase condition. Our scheme provides a flexible and efficient method for solid state quantum single photon sources.

Photon blockade via quantum interference in a strong coupling qubit-cavity system.

In a coherently-driven nanocavity QED system, the one-photon blockade via quantum interference is investigated by the modified Lindblad master equation and without using the secular approximation as well. Based on the dressed bases of the Rabi Hamiltonian, a modified Lindblad master equation is obtained, which is valid for any arbitrary degree of the qubit-cavity interaction. It is found that the damping coefficients are very sensitive to interaction strength between the qubit and the cavity mode. How to enhance the one-photon blockade by using the quantum interference effect is discussed with the generalized second-order correlation function and the second-order perturbation in the five-state truncation of the Hilbert space. It is found that, under suitable pump or detection conditions, a strong one-photon blockade can be realized by completely eliminating the two-photon emission. Moreover, even for a strong cavity damping rate, there exhibits a large number of cavity photons by utilizing the quantum interference mechanism.

Landau–Zener–Stueckelberg interferometry with driving fields in the quantum regime

We analyze the dynamics of a two-level quantum system (TLS) under the influence of a strong sinusoidal driving signal whose origin is the interaction of the two-level system with a quantum field. In this approach the driving field is replaced by a harmonic oscillator that is either strongly coupled to the TLS or populated with a large number of photons. Starting from the Rabi model, we derive expressions for the TLS’s oscillation frequencies and compare the results with those obtained from the model where the driving signal is treated classically. We show that in the limits of weak coupling and large photon number, the well-known expression for the Rabi frequency in the strong driving regime is recovered. In the opposite limit of strong coupling and small photon number, we find differences between the predictions of the semiclassical and quantum models. The results of the quantum picture can therefore be understood as Landau–Zener–Stueckelberg interferometry in the fully quantum regime.

Indirect methods to control population distribution in a large spin system

We demonstrate how a large spin system () with the ground and first excited state separated by a seven-photon transition exhibits nonequilibrium thermodynamic properties and how the population distribution may be manipulated using coupling between energy levels. The first method involves non-adiabatic passage through an avoided level crossing controlled with an external DC magnetic field and the resulting Landau–Zener transition. The second method is based on external cavity pumping to a higher energy state hybridised with another state that is two single-photon transitions away from the ground state. The results are confirmed experimentally with a Gd3+ impurity ion ensemble in a YVO4 crystal cooled to 20 mK, which also acts as a microwave photonic whispering gallery mode resonator. Extremely long lifetimes are observed due to the large number of photons required for the transition between the ground and first excited states.

Generating double NOON states of photons in circuit QED

To generate a NOON state with a large photon number $N$, the number of operational steps could be large and the fidelity will decrease rapidly with $N$. Here we propose a method to generate a new type of quantum entangled states, $(|NN00\rangle+|00NN\rangle)/\sqrt{2}$ called "double NOON" states, with a setup of two superconducting flux qutrits and five circuit cavities. This scheme operates essentially by employing a two-photon process, i.e., two photons are simultaneously and separately emitted into two cavities when each coupler qutrit is initially in a higher-energy excited state. As a consequence, the "double" NOON state creation needs only $N$+2 operational steps. One application of double NOON states is to get a phase error of $1/(2N)$ in phase measurement. In comparison, to achieve the same error, a normal NOON state of the form $(|2N,0\rangle+|0,2N\rangle)/\sqrt{2}$ is needed, which requires at least $2N$ operational steps to prepare by using the existing schemes. Our numerical simulation demonstrates that high-fidelity generation of the double NOON states with $N\leq 10$ even for the imperfect devices is feasible with the present circuit QED technique.

Diverging light pulses in vacuum: Lorentz-invariant mass and mean propagation speed

We show that the concept of the Lorentz-invariant mass of groups of particles can be applied to light pulses consisting of very large but finite numbers of noncollinear photons. Explicit expressions are found for the invariant mass of this manifold of photons for the case of diverging Gaussian light pulses propagating in vacuum. As the found invariant mass is finite, the light pulses propagate in vacuum with a speed somewhat smaller than the light speed. A small difference between the light speed and the beam-propagation velocity is found to be directly related to the invariant mass of a pulse. Focusing and/or defocusing light pulses is shown to strengthen the effect in which the pulse slows down while the pulse invariant mass increases. A scheme for measuring these quantities experimentally is proposed and discussed.