Quantum Coherence Phenomena Research Articles

Long-lived quantum coherence in a two-level semiconductor quantum dot

In this paper, we present an analytical solution for the system of two-level semiconductor quantum dot. In addition, we discuss the rates of the photon radiative and phonon radiationless transitions from the excited state $$ (\alpha _{12}, \alpha _{21}),$$ the rate of processes of pure dephasing $$ (\gamma )$$ , the detuning parameter ( $$\Delta $$ ) and the Rabi frequency ( $$\Omega $$ ), on the atomic occupation probabilities ( $$\rho _{11}(t)$$ and $$\rho _{22}(t)),$$ the atomic population inversion ( $$\rho _{z}(t)),$$ the purity ( $$P_{A}(t)),$$ the von Neumann entropy (S(t)) and the information entropies ( $$H(\sigma _{x}),$$ $$H(\sigma _{y})$$ and $$H(\sigma _{z}))$$ . We clearly observe the emergence of long-lived quantum coherence phenomenon in all the curves for some special cases of $$\alpha _{12},$$ $$\alpha _{21}$$ , $$\gamma $$ , $$\Delta $$ and $$ \Omega .$$ Besides, the decay phenomenon is quite evident in the purity curves, which can be simply controlled by changing the values of $$\alpha _{12},$$ $$ \alpha _{21}$$ and $$\gamma .$$

Magnon Bose–Einstein Condensate and Supercurrents Over a Wide Temperature Range

Magnon Bose–Einstein Condensates (BECs) and supercurrents are coherent quantum phenomena, which appear on a macroscopic scale in parametrically populated solid state spin systems. One of the most fascinating and attractive features of these processes is the possibility of magnon condensation and supercurrent excitation even at room temperature. At the same time, valuable information about a magnon BEC state, such as its lifetime, its formation threshold, and coherence, is provided by experiments at various temperatures. Here, we use Brillouin Light Scattering (BLS) spectroscopy for the investigation of the magnon BEC dynamics in a single-crystal film of yttrium iron garnet in a wide temperature range from 30 K to 380K. By comparing the BLS results with previous microwave measurements, we revealed the direct relation between the damping of the condensed and the parametrically injected magnons. The enhanced supercurrent dynamics was detected at 180 K near the minimum of BEC damping.

Linear and nonlinear Herzberg−Teller vibronic coupling effects. II: Hole-burning and fluorescence line narrowing spectroscopy

Part I of this series showed that Herzberg-Teller vibronic coupling manifests itself in linear spectroscopy through the breakdown of the mirror image symmetry between the absorption and emission spectra, whereby a nuclear exponential function was used to represent the molecular electronic transition dipole moment. This part tests the applicability of the framework developed in Paper I to absorption-emission asymmetry in nonlinear signals such as hole-burned and fluorescence line narrowed spectra. Model calculations of nonlinear absorption and emission spectra showing asymmetry is provided. Hole-burning and fluorescence line narrowing signals are to exemplify nonlinear absorption and emission spectra so as to reveal the anticipated asymmetry in 4-wave mixing experiments, and probe the consequent zero-phonon hole and the phonon-sideband hole. These calculations prove to be efficient and fast, exhibiting remarkable numerical stability. The observation of richer phonon-side band (PSB) in linear spectra, phono-side band hole (PSBH) in Hole-burning and fluorescence line narrowing signals, and emergence of new quantum beats over longer time scale (despite the dissipative medium) under the non-Condon regime are linked to the long quantum coherence phenomenon and stimulated photon peak shift in photosynthetic systems.

High temperature singlet-based magnetism from Hund\u2019s rule correlations

Uranium compounds can manifest a wide range of fascinating many-body phenomena, and are often thought to be poised at a crossover between localized and itinerant regimes for 5f electrons. The antiferromagnetic dipnictide USb2 has been of recent interest due to the discovery of rich proximate phase diagrams and unusual quantum coherence phenomena. Here, linear-dichroic X-ray absorption and elastic neutron scattering are used to characterize electronic symmetries on uranium in USb2 and isostructural UBi2. Of these two materials, only USb2 is found to enable strong Hund’s rule alignment of local magnetic degrees of freedom, and to undergo distinctive changes in local atomic multiplet symmetry across the magnetic phase transition. Theoretical analysis reveals that these and other anomalous properties of the material may be understood by attributing it as the first known high temperature realization of a singlet ground state magnet, in which magnetism occurs through a process that resembles exciton condensation.

Transport and Quantum Coherence in Graphene Rings: Aharonov–Bohm Oscillations, Klein Tunneling, and Particle Localization

Simulating quantum transport through mesoscopic, ring-shaped graphene structures, we address various quantum coherence and interference phenomena. First, a perpendicular magnetic field, penetrating the graphene ring, gives rise to Aharonov–Bohm oscillations in the conductance as a function of the magnetic flux, on top of the universal conductance fluctuations. At very high fluxes, the interference gets suppressed and quantum Hall edge channels develop. Second, applying an electrostatic potential to one of the ring arms, $$nn'n$$ - or npn-junctions can be realized with particle transmission due to normal tunneling or Klein tunneling. In the latter case, the Aharonov–Bohm oscillations weaken for smooth barriers. Third, if potential disorder comes in to play, both Aharonov–Bohm and Klein tunneling effects rate down, up to the point where particle localization sets in.

Quantum coherence phenomenon in disordered Bi2SeTe2 topological single crystal: effect of annealing

We report a comparative magnetotransport study on pristine and annealed Bi2SeTe2 single crystals. The pristine sample shows a metallic trend from 300 to 180 K, and an insulating behavior for T < 180 K, whereas the annealed sample exhibits an insulating nature in the entire 4.2–300 K temperature range. Magnetoresistance (MR) of pristine and annealed samples reveals contrasting behaviour as a function of temperature (T) and magnetic field (B). At 4.2 K, the pristine sample shows weak antilocalization (WAL) behavior at low fields and transforms to weak localization (WL) behavior (negative MR) for B > 2.5 T. Further, the quantum MR behaviours seen at low temperature gradually transform to classical B2 dependent upon increasing the temperatures. In contrast, the annealed sample shows a WAL at small field superimposed on a parabolic feature for B > ±4 T at low temperatures (T < 20 K). It shows a linear MR at intermediate temperatures (40 K < T < 100 K) and a parabolic MR at temperatures T > 100 K. Hall measurements on both samples exhibit a nonlinear behavior at 4.2 K pointing to the existence of two types of carriers with different mobility. The annealed sample also shows a drastic decrease in mobility by one order of magnitude and a reduction in Ioffe–Regel parameter (kFl) by a factor of ~3. Disorder-induced localization of bulk carriers and its coexistence with localization-immune surface carriers at low T leads to WAL and WL. MR observed in the annealed sample can be attributed to the presence of both quantum–classical contribution and has been analysed using the Hikami–Larkin–Nagaoka (HLN) equation.

Temperature and wall coating dependence of alkali vapor transport speed in micron-scale capillaries

The impact of storage temperature and wall coatings on alkali vapor transport through micron-scale glass capillaries is analyzed. Glass microbore tubing, chromatography vials, and copper tubing are assembled into closed atomic spectroscopy units with varying capillary lengths and inner diameters. Such devices serve as valuable test models for integrated atomic spectroscopy platforms that rely on hollow-core optical waveguides for chip-scale implementation of quantum coherence phenomena such as slow and stopped light. The inside surface of the systems are coated with dimethyldichlorosilane (DMDCS) after which the system is loaded with rubidium vapor and hermetically sealed. The loaded units are stored in a tube furnace at elevated temperatures and tested daily for absorption over several weeks. Both a wall coating of DMDCS and higher storage temperature increases the transport speed of Rb vapor. The limits and implications of these results are discussed and compared to an expected theoretical model. Suggestions for increasing transport speed are given.

Control of the Oscillatory Interlayer Exchange Interaction with Terahertz Radiation.

The oscillatory interlayer exchange interaction between two magnetic layers separated by a metallic spacer is one of the few coherent quantum phenomena that persists at room temperature. Here, we show that this interaction can be controlled dynamically by illuminating the sample (e.g., a spin valve) with radiation in the 10-100THz range. We predict that the exchange interaction can be changed from ferromagnetic to antiferromagnetic (and vice versa) by tuning the amplitude and/or the frequency of the radiation. Our chief theoretical result is an expression that relates the dynamical exchange interaction to the static one that has already been extensively measured.

Coherent perfect absorption and transmission of a generalized three-mode cavity optico-mechanical system

With the rapid development of nano-physics and quantum optics, optico-mechanical coupling system is developing toward the miniaturization and lightweight. The physical characteristics of optical cavity and applications of optic-mechanical devices have received much attention. In this paper, a generalized three-mode cavity optico-mechanical system is presented, the steady-state responses of the system to the characteristics of weak detection of light absorption and dispersion in several different coherent driving modes are studied. Situated in the middle of system is a portable total reflection mechanical oscillator with a reflectance of 100%, and located on each side is a fixed optical cavity mirror with partial transmittance, Three-mode cavity optical mechanical system consists of fixed-mirror, removable-vibrator, fixed-mirror structure. in which the two optical cavities are coupled by coupling a stronger control field and weak probe light with the same mechanical oscillator. Analysis and numerical results show that under the mechanism with different parameters, due to nonlinear effect of pressure, in the three-mode cavity optical mechanical system, there appear some interesting quantum coherent phenomena such as coherent perfect absorption, coherent perfect transmission and coherent perfect synthesis. When coherent perfect absorption occurs, the mutual conversion between input signal power full-field energies and oscillator vibration of internal coherence can be realized, and the law of conservation of energy is satisfied. When relaxation rate due to mechanical oscillator is very small, the coherent perfect transmission is completely transmitted from the system side of the input field to the other side in the case of no loss of energy. And mechanical relaxation rate of the oscillator approaches to zero in the middle, which can ensure that the perfect transmission of the detection field takes place on one side, and the field total reflection and coherent perfect synthesis happen on the other side of. In addition, we alsofind that the adjustment of coupling between cavity and cavity can change the intensity of the probe field of quantum coherent control thereby realizing that the output of the detection field is transformed between coherent perfect absorption and coherence transmission; through simple phase modulation the output direction and input direction of detection field for left cavity-right cavity can swap mutually. So, these dynamic controls in quantum information networks can be used to construct some optical devices with special functions, such as photon switch, photo router, photon exchange machine, etc.

Measurement of weak static magnetic field with nitrogen-vacancy color center

基于金刚石氮-空位色心对精确测量微弱静磁场进行了探索.金刚石氮-空位色心电子自旋的退相干时间高度依赖于外磁场，而不同的退相干特征时间对磁场的灵敏度不同.对金刚石氮-空位色心电子自旋在不同强度外磁场下的退相干过程进行模拟，得到不同退相干特征时间与磁场大小的高准确度关系，提出了基于响应度最高的退相干特征时间测量静态弱磁场大小和方向的方法，并分析了该方法测量静态弱磁场的灵敏度，证明该方法的测量灵敏度比一般磁场测量仪器更高.

Microwave control of the superconducting proximity effect and minigap in magnetic and normal metals.

We demonstrate theoretically that microwave radiation applied to superconducting proximity structures controls the minigap and other spectral features in the density of states of normal and magnetic metals, respectively. Considering both a bilayer and Josephson junction geometry, we show that microwaves with frequency ω qualitatively alters the spectral properties of the system: inducing a series of resonances, controlling the minigap size Emg, and even replacing the minigap with a strong peak of quasiparticle accumulation at zero energy when ω = Emg. The interaction between light and Cooper pairs may thus open a route to active control of quantum coherent phenomena in superconducting proximity structures.

International Conference on the Frontiers in Atomic, Molecular, and Optical Physics (AMO2016)

Atoms, molecules, and light have been at the forefront of understanding quantum mechanics, since its discovery over 100 years ago. Since then the field has progressed from understanding the most fundamental aspects of how particles behave under quantum mechanics to controlling individual atoms for creating new technologies. While matter and light are from ordinary experience rather different, with today's control of coherent quantum phenomena many of the ideas freely cross their respective boundaries. Some of the topics that will be covered at the conference include, but are not limited to, cold atoms & cold molecules, ultrafast & precision spectroscopy, quantum manipulation & precision measurement, quantum computing & quantum communication, and quantum metrology. In this conference we aim to bring together the leading experts working in the frontiers of atomic, molecular, and optical systems.Scientific Committee:Guoxiang HuangDirector,NYU-ECNU Institute of Physics at NYU Shanghai;Professor of PhysicsDepartment of Physics and State Key Laboratory of Precision Spectroscopy East China Normal UniversityDaniel L. SteinDirector,NYU-ECNU Institute of Physics at NYU Shanghai;Professor of Physics and Mathematics Departments of Physics and Mathematics, NYUJian WuDirector, Professor of PhysicsState Key Laboratory of Precision SpectroscopyEast China Normal UniversityE WuResearcherState Key Laboratory of Precision Spectroscopy East China Normal UniversityHaibin WuProfessor of PhysicsState Key Laboratory of Precision Spectroscopy East China Normal UniversityTim ByrnesAssistant Professor of Physics at NYU ShanghaiInvited Speakers:Jurgen Appel (Copenhagen, Denmark)Luiz Davidovich (Universidade Federal Do Rio De Janeiro, Brazil) Jonathan Dowling (LSU, USA)Luming Duan (Michigan, USA)Claude Fabre (Universite Pierre Et Marie Curie, France)Elisabeth Giacobino (CNRS Laboratoire Kastler-Brossel, France)Rudolf Grimm (Innsbruck, Austria)Fedor Jelezko (Ulm, Germany)Ruxin Li (SIOM, China)Peter Van Loock (Mainz, Germany)Longsheng Ma (ECNU, China)Jian-Wei Pan (USTC, China)Jean-Francois Roch (ENS Cachan, France)Bao-Sen Shi (USTC, China)Masahito Ueda (Tokyo, Japan)Pengjun Wang (Shanxi, China)Jorg Wrachtrup (Stuttgart, Germany)Min Xiao (Arkansas, USA)Lei Xu (Fudan, China)Li You (Tsinghua, China)

Qubit lattice coherence induced by electromagnetic pulses in superconducting metamaterials.

Quantum bits (qubits) are at the heart of quantum information processing schemes. Currently, solid-state qubits, and in particular the superconducting ones, seem to satisfy the requirements for being the building blocks of viable quantum computers, since they exhibit relatively long coherence times, extremely low dissipation, and scalability. The possibility of achieving quantum coherence in macroscopic circuits comprising Josephson junctions, envisioned by Legett in the 1980’s, was demonstrated for the first time in a charge qubit; since then, the exploitation of macroscopic quantum effects in low-capacitance Josephson junction circuits allowed for the realization of several kinds of superconducting qubits. Furthermore, coupling between qubits has been successfully achieved that was followed by the construction of multiple-qubit logic gates and the implementation of several algorithms. Here it is demonstrated that induced qubit lattice coherence as well as two remarkable quantum coherent optical phenomena, i.e., self-induced transparency and Dicke-type superradiance, may occur during light-pulse propagation in quantum metamaterials comprising superconducting charge qubits. The generated qubit lattice pulse forms a compound ”quantum breather” that propagates in synchrony with the electromagnetic pulse. The experimental confirmation of such effects in superconducting quantum metamaterials may open a new pathway to potentially powerful quantum computing.

Magnetoelectric Mapping as Observed in Quantum Coherence Phenomena under Strong Spin-Orbit Interaction

A magnetoelectric mapping is demonstrated between dephasing effects of the magnetic vector potential and effects of an effective vector potential describing spin-orbit interaction. The experiments use spin-dependent mesoscopic quantum transport experiments on the narrow-gap semiconductor InSb and the semimetal Bi, both materials with strong spin-orbit interaction. The spin-orbit-induced antilocalization signature in transport allows determination of spin coherence lengths in narrow InSb and Bi wires. Spin coherence lengths are observed to increase with decreasing wire widths. The geometrical effect of width can be understood from the magnetoelectric duality between the Aharonov-Bohm phase and the Aharonov-Casher phase.

Breakthroughs in Photonics 2014: Time-Scale-Dependent Nonlinear Dynamics in InAs/InP Quantum Dot Gain Media: From High-Speed Modulation to Coherent Light–Matter Interactions

The dynamical properties of InP-based quantum dot (QD) gain media are surveyed and analyzed for three time scales ranging from tens of picoseconds to less than 200 fs, where quantum coherent phenomena are observable. Each of these time scales determines the important properties of QD devices, i.e., modulation capabilities, nonlinear gain, and coherent light-matter interactions. Experimental investigations and modeling results are described, highlighting the state of the art in QD devices for the important 1550-nm telecom wavelength range.

Phase-dependent optical response properties in an optomechanical system by coherently driving the mechanical resonator

We explore theoretically the optical response properties in an optomechanical system under electromagneti- cally induced transparency condition but with the mechanical resonator being driven by an additional coherent field. In this configuration, more complex quantum coherent and interference phenomena occur. In partic- ular, we find that the probe transmission spectra depend on the total phase of the applied fields. Our study also provides an efficient way to control propagation of amplification.

Few-Electron Ultrastrong Light-Matter Coupling in a QuantumLCCircuit

Future systems for quantum information processing will rely on coherent quantum phenomena, such as the coupling between light and matter. Using a quantum well within a capacitor to study how atomic physics and condensed matter physics are linked, researchers suggest a device architecture for semiconductor-based quantum processing.

Coherent control in a semiconductor optical amplifier operating at room temperature

Quantum decoherence times in semiconductors are extremely short, particularly at room temperature where the quantum phase is completely erased in a fraction of a picosecond. However, they are still of finite duration during which the quantum phase is well defined and can be tailored. Recently, we demonstrated that quantum coherent phenomena can be easily accessed by examining the phase and amplitude of an optical pulse following propagation along a room temperature semiconductor optical amplifier. Taking the form of Rabi oscillations, these recent observations enabled to decipher the time evolution of the ensemble states. Here we demonstrate the Ramsey analogous experiment known as coherent control. Remarkably, coherent control occurs even under room temperature conditions and enables to directly resolve the dephasing times. These results may open a new way for the realization of room temperature semiconductor-based ultra-high speed quantum processors with all the advantages of upscaling and low-cost manufacturing.

Integrated polarization rotator/converter by stimulated Raman adiabatic passage

We proposed a polarization rotator inspired by stimulated Raman adiabatic passage model from quantum optics, which is composed of a signal waveguide and an ancillary waveguide. The two orthogonal modes in signal waveguide and the oblique mode in ancillary waveguide form a Λ-type three-level system. By controlling the width of signal waveguide and the gap between two waveguides, adiabatic conversion between two orthogonal modes can be realized in the signal waveguide. With such adiabatic passage, polarization conversion is completed within 150 μm length, with the efficiencies over 99% for both conversions between horizontal polarization and vertical polarization. In addition, such a polarization rotator is quite robust against fabrication error, allowing a wide range of tolerances for the rotator geometric parameters. Our work is not only significative to photonic simulations of coherent quantum phenomena with engineered photonic waveguides, but also enlightens the practical applications of these phenomena in optical device designs.

Effects of quantum coherence in metalloprotein electron transfer

Many intramolecular electron transfer (ET) reactions in biology are mediated by metal centers in proteins. This process is commonly described by a model of diffusive hopping according to the semiclassical theories of Marcus and Hopfield. However, recent studies have raised the possibility that nontrivial quantum mechanical effects play a functioning role in certain biomolecular processes. Here, we investigate the potential effects of quantum coherence in biological ET by extending the semiclassical model to allow for the possibility of quantum coherent phenomena using a quantum master equation based on the Holstein Hamiltonian. We test the model on the structurally defined chain of seven iron-sulfur clusters in nicotinamide adenine dinucleotide plus hydrogen:ubiquinone oxidoreductase (complex I), a crucial respiratory enzyme and one of the longest chains of metal centers in biology. Using experimental parameters where possible, we find that, in limited circumstances, a small quantum mechanical contribution can provide a marked increase in the ET rate above the semiclassical diffusive-hopping rate. Under typical biological conditions, our model reduces to well-known diffusive behavior.