Collective Quantum States Research Articles

Collectively induced transparency and absorption in waveguide quantum electrodynamics with Bragg atom arrays

Collective quantum states, such as subradiant and superradiant states, are useful for controlling optical responses in many-body quantum systems. In this work, we study novel collective quantum phenomena in waveguide-coupled Bragg atom arrays with inhomogeneous frequencies. For atoms without free-space dissipation, collectively induced transparency is produced by destructive quantum interference between subradiant and superradiant states. In a large Bragg atom array, multi-frequency photon transparency can be obtained by considering atoms with different frequencies. Interestingly, we find collectively induced absorption (CIA) by studying the influence of free-space dissipation on photon transport. Tunable atomic frequencies nontrivially modify decay rates of subradiant states. When the decay rate of a subradiant state equals to the free-space dissipation, photon absorption can reach a limit at a certain frequency. In other words, photon absorption is enhanced with low free-space dissipation, distinct from previous photon detection schemes. We also show multi-frequency CIA by properly adjusting atomic frequencies. Our work presents a way to manipulate collective quantum states and exotic optical properties in waveguide quantum electrodynamics (QED) systems.

Two-photon pumped exciton-polariton condensation

Two-photon absorption (TPA) allows accessing “dark” states of matter that are otherwise inaccessible to light, which serve as important building blocks for quantum information processing. In a semiconductor microcavity, TPA-driven condensation of strongly coupled light-matter exciton–polaritons can enable new solid-state quantum simulations of “dark” state-condensate interactions and was predicted to stimulate THz emission. Here, we report the first observation of two-photon-pumped polariton condensation, demonstrated by angle-resolved photoluminescence in a GaAs-based microcavity. TPA is evidenced in the quadratic emission dependence on pump power below and above the condensation threshold, and second-harmonic generation is ruled out by both this threshold behavior and by the emission peak energy showing no dependence on pump photon energy. Our results pave the way toward novel polariton-based sources and solid-state coherent control of collective quantum states with individual two-level systems.

ENGINEERED NANO-MATERIALS FOR ENERGY AND THEIR POTENTIAL IMPACT ON ACTUAL ENVIRONMENTAL ISSUES

It is known for more than 2000 years that Damascus swords’ performances were not possible without the existence and usage of the “Damascus steel”, the first man made nano-hetero structural material that generalized is clearly showing that materials determine ultimate properties of the objects that made of. The actual world energy is manly based carbon emission materials, as coal, heavy oil, methane gas, with negative environment impact. Solar, wind and geothermal energy have also a negative impact on environment and have to be smartly used to minimize it. Nuclear energy, has lower CO2 emission, but because it is in its infancy it is complex, expensive and raises security and proliferation issues, has the potential for large scale accidents, and generates difficulties in dealing with waste fuel dispositioning.The novel developed families of engineered nano-materials, eliminate all the drawbacks of the actual nuclear power, rendering it among the most efficient and environmental friendly energy source. We learned from the global warming that the amount of energy man can produce on Earth is limited at 0.1% of sun delivered on Earth energy of 170 PW, which is of 200 TW, about 100 times more than today if it is chemical pollution free. Thermal pollution remains in place, therefore the upper clean power limit acceptable for the planet is at about 100 TW.The novel nuclear materials were developed in 6 families, each of them bringing in harmony a nuclear agent active inside that material as:- Micro-hetero structures, generally called “cer-Liq-Mesh”, that self-separates the fission products from the nuclear fuel and minimizes their fuel damage, allowing breed&burn to near perfect burning;- Nano-hetero structures generically called “CIci”, that form a super-capacitor, charged by nuclear energy and directly discharged as electricity;- Nano-clustered structure that enhances self-separation of transmutation products;- Fractal immiscible materials with radiation damage self-repairing capabilities eliminating the need for re-cladding in near perfect burning structures- Nano-structures with active NEMS used as fast control of nuclear reactivity by guiding neutrons in desired directions or ultralight shielding for mobile reactors.- Nano-structures that create active-quantum-nuclear-environment for long range nuclear reactions control by using quantum states entanglement and collective quantum states control.The use of these advanced materials in future nuclear energy related application will render a high efficiency, minimal nuclear waste, and optimal nuclear fuel cycle, delivering the needed planetary clean energy at will for the next 10,000 years.

Bulk Photovoltaic Effect Driven by Collective Excitations in a Correlated Insulator.

We investigate the bulk photovoltaic effect, which rectifies light into electric current, in a collective quantum state with correlation driven electronic ferroelectricity. We show via explicit real-time dynamical calculations that the effect of the applied electric field on the electronic order parameter leads to a strong enhancement of the bulk photovoltaic effect relative to the values obtained in a conventional insulator. The enhancements include both resonant enhancements at sub-band-gap frequencies, arising from excitation of optically active collective modes, and broadband enhancements arising from nonresonant deformations of the electronic order. The deformable electronic order parameter produces an injection current contribution to the bulk photovoltaic effect that is entirely absent in a rigid-band approximation to a time-reversal symmetric material. Our findings establish that correlation effects can lead to the bulk photovoltaic effect and demonstrate that the collective behavior of ordered states can yield large nonlinear optical responses.

Two-gap to single-gap superconducting transition on a honeycomb lattice in Ca1−xSrxAlSi

It is a well-established fact that the physical properties of compounds follow their crystal symmetries. This has especially pronounced implications on emergent collective quantum states in materials. Specifically, the effect of crystal symmetries on the properties of superconductors is widely appreciated, although the clarification of this relationship is a core effort of on-going research. Emergent phenomena on honeycomb lattices are of special interest, as they can give rise to spectacular phenomenology, as manifested by the recent discovery of correlated states in magic-angle graphene, or by the high-temperature superconductivity in MgB$_2$. Here, we report on the structural and microscopic superconducting properties of a class of ternary superconductors with Al/Si honeycomb layers, i.e. Ca$_{1-x}$Sr$_{x}$AlSi. We show that this solid solution is a remarkable model system with a highly tunable two-gap to single-gap superconducting system on a honeycomb lattice, where the superconductivity is enhanced by a subtle structural instability, i.e. the buckling of the Al/Si layers.

High-temperature superfluorescence in methyl ammonium lead iodide

Light–matter interactions can create and manipulate collective many-body phases in solids1,2,3, which are promising for the realization of emerging quantum applications. However, in most cases, these collective quantum states are fragile, with a short decoherence and dephasing time, limiting their existence to precision tailored structures under delicate conditions such as cryogenic temperatures and/or high magnetic fields. In this work, we discovered that the archetypal hybrid perovskite, MAPbI3 thin film, exhibits such a collective coherent quantum many-body phase, namely superfluorescence, at 78 K and above. Pulsed laser excitation first creates a population of high-energy electron–hole pairs, which quickly relax to lower energy domains and then develop a macroscopic quantum coherence through spontaneous synchronization. The excitation fluence dependence of the spectroscopic features and the population kinetics in such films unambiguously confirm all the well-known characteristics of superfluorescence. These results show that the creation and manipulation of collective coherent states in hybrid perovskites can be used as the basic building blocks for quantum applications4,5.

Advances in Rare-Earth Tritelluride Quantum Materials: Structure, Properties, and Synthesis.

A distinct class of 2D layered quantum materials with the chemical formula of RTe3 (R = lanthanide) has gained significant attention owing to the occurrence of collective quantum states, superconductivity, charge density waves (CDW), spin density waves, and other advanced quantum properties. To study the Fermi surface nesting driven CDW formation, the layered RTe3 family stages an excellent low dimensional genre system. In addition to the primary energy gap feature observed at higher energy, optical spectroscopy study on some RTe3 evidence a second CDW energy gap structure indicating the occurrence of multiple CDW ordering even with light and intermediate RTe3 compounds. Here, a comprehensive review of the fundamentals of RTe3 layered tritelluride materials is presented with a special focus on the recent advances made in electronic structure, CDW transition, superconductivity, magnetic properties of these unique quantum materials. A detailed description of successful synthesis routes including the flux method, self‐flux method, and CVT along with potential applications is summarized.

Coherent control of collective nuclear quantum states via transient magnons.

Ultrafast and precise control of quantum systems at x-ray energies involves photons with oscillation periods below 1 as. Coherent dynamic control of quantum systems at these energies is one of the major challenges in hard x-ray quantum optics. Here, we demonstrate that the phase of a quantum system embedded in a solid can be coherently controlled via a quasi-particle with subattosecond accuracy. In particular, we tune the quantum phase of a collectively excited nuclear state via transient magnons with a precision of 1 zs and a timing stability below 50 ys. These small temporal shifts are monitored interferometrically via quantum beats between different hyperfine-split levels. The experiment demonstrates zeptosecond interferometry and shows that transient quasi-particles enable accurate control of quantum systems embedded in condensed matter environments.

Continuous Protection of a Collective State from Inhomogeneous Dephasing

We introduce and demonstrate a scheme for eliminating the inhomogeneous dephasing of a collective quantum state. The scheme employs off-resonant fields that continuously dress the collective state with an auxiliary sensor state, which has an enhanced and opposite sensitivity to the same source of inhomogeneity. We derive the optimal conditions under which the dressed state is fully protected from dephasing when using either one or two dressing fields. The latter provides better protection, circumvents qubit phase rotation, and suppresses the sensitivity to drive noise. We further derive expressions for all residual, higher-order sensitivities. We experimentally study the scheme by protecting a collective excitation of an atomic ensemble, where inhomogeneous dephasing originates from thermal motion. Using photon storage and retrieval, we demonstrate complete suppression of inhomogeneous dephasing and, consequently, a prolonged memory time. Our scheme may be applied to eliminate motional dephasing in other systems, improving the performance of quantum gates and memories with neutral atoms. It is also generally applicable to various gas, solid, and engineered systems, where sensitivity to variations in time, space, or other domains limits possible scale-up of the system.Received 23 April 2020Revised 1 October 2020Accepted 23 November 2020DOI:https://doi.org/10.1103/PhysRevX.11.011008Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasOptical quantum information processingQuantum information with atoms & lightQuantum memoriesQuantum opticsAtomic, Molecular & OpticalQuantum Information

Single-water-dipole-layer-driven Reversible Charge Order Transition in 1T-TaS2.

Water-solid interactions are crucial for many fundamental phenomena and technological processes. Here, we report a scanning tunneling microscopy study about the charge density wave (CDW) transition in 1T-TaS2 driven by a single water dipole layer. At low temperature, pristine 1T-TaS2 is a prototypical CDW compound with × charge order. After growing a highly ordered water adlayer, a new charge order with 3 × 3 periodicity emerges on water-covered 1T-TaS2. After water desorption, the entire 1T-TaS2 surface appears as localized × CDW domains that are separated by residual-water-cluster-pinned CDW domain walls. First-principles calculations show that the electric dipole moments in the water adlayer attract electrons to the top layer of 1T-TaS2, which shifts the phonon softening mode and induces the × to 3 × 3 charge order transition. Our results pave the way for creating new collective quantum states of matter with a molecular dipole layer.

Quartet states in two-electron quantum dots in bilayer graphene

Trapping electrons in quantum dots and controlling their collective quantum states is crucial for converting semiconductor structures into bits of quantum information processing. Here, we study single- and two-particle states in quantum dots formed in gapped bilayer graphene (BLG), where the electron's valley states appear in pair with their spin quantum number and we analyse spin- and valley-singlet and triplet states for various BLG and dot parameters, as well as two-particle interaction strength and external magnetic field.

Collapse of layer dimerization in the photo-induced hidden state of 1T-TaS2

Photo-induced switching between collective quantum states of matter is a fascinating rising field with exciting opportunities for novel technologies. Presently, very intensively studied examples in this regard are nanometer-thick single crystals of the layered material 1T-TaS2, where picosecond laser pulses can trigger a fully reversible insulator-to-metal transition (IMT). This IMT is believed to be connected to the switching between metastable collective quantum states, but the microscopic nature of this so-called hidden quantum state remained largely elusive up to now. Here, we characterize the hidden quantum state of 1T-TaS2 by means of state-of-the-art x-ray diffraction and show that the laser-driven IMT involves a marked rearrangement of the charge and orbital order in the direction perpendicular to the TaS2-layers. More specifically, we identify the collapse of interlayer molecular orbital dimers as a key mechanism for this non-thermal collective transition between two truly long-range ordered electronic crystals.

Quantum state preparation of an atomic ensemble via cavity-assisted homodyne measurement

The quantum spin states of an atomic ensemble are of special interest to both fundamental studies and precision measurement applications. Here, we propose a scheme to prepare collective quantum states of an atomic ensemble placed in an optical cavity via homodyne measurement of a probing light field. The effective interactions of atoms mediated by photons are enhanced by the optical cavity, and the output probe light could also be entangled with the collective spin states. By selectively measuring the quadrature of the output light, we can prepare various quantum states, including superposition states of Dicke states and Dicke squeezed states. It is also demonstrated that the fidelity of the prepared quantum state can be enhanced by repetitive homodyne detection and using longer probe laser pulses. With the experimental parameters, we discuss some imperfections, including background noise, fluctuation of the measurement outcomes, and free-space scattering.We believe that our scheme should be feasible for experimental realization with current technologies, which may be used in the future study of quantum mechanics and quantum metrology.

Intervalley Quantum Coherence Transfer and Coherently-Induced Chiral Plasmon Fields in WS2–Metallic Nanoantenna Systems

We theoretically show that when a hybrid system consisting of a transition metal dichalcogenide monolayer (WS2) and an achiral metallic nanoantenna interacts with a circularly polarized laser field, plasmonically mediated coherently induced processes can transfer quantum coherence from one valley (K or K′) to another. This leads to spin-valley-dependent plasmon field enhancement and coherently driven energy transfer from the WS2 monolayer to the nanoantenna. For the case when the incident laser is right circularly polarized (σ+), we study intervalley transfer of excitation and polarization from K to K′ valleys while mapping the evolution of the Stokes vectors associated with the emission of the WS2 monolayer. This is done as we explore the impact of variation of the laser frequency and intensity on K–K′ coupling. Our results show a formation of collective quantum states and an abrupt transition between these states at a certain frequency. We demonstrate that, as such a transition happens, the Stokes vecto...

Spectroscopic fingerprints of many-body renormalization in 1T−TiSe2

We have employed high resolution angle resolved photoemission spectroscopy (ARPES) measurements to investigate many-body renormalizations of the single-particle excitations in $1T$-TiSe$_2$. The energy distribution curves of the ARPES data reveal intrinsic peak-dip-hump feature, while the electronic dispersion derived from the momentum distribution curves of the data highlights, for the first time, multiple kink structures. These are canonical signatures of a coupling between the electronic degrees of freedom and some Bosonic mode in the system. We demonstrate this using a model calculation of the single-particle spectral function at the presence of an electron-Boson coupling. From the self-energy analysis of our ARPES data, we discern some of the critical energy scales of the involved Bosonic mode, which are $\sim$15 and 26 meV. Based on a comparison between these energies and the characteristic energy scales of our Raman scattering data, we identify these Bosonic modes as Raman active breathing (${\text{A}}_\text{1g}$) and shear (${\text{E}}_\text{g}$) modes, respectively. Direct observation of the band-renormalization due to electron-phonon coupling increases the possibility that electron-phonon interactions are central to the collective quantum states such as charge density wave (CDW) and superconductivity in the compounds based on $1T$-TiSe$_2$.

Rephasing efficiency of sequences of phased pulses in spin-echo and light-storage experiments

We investigate the rephasing efficiency of sequences of phased pulses for spin echoes and light storage by electromagnetically induced transparency (EIT). We derive a simple theoretical model and show that the rephasing efficiency is very sensitive to the phases of the imperfect rephasing pulses. The obtained efficiency differs substantially for spin echoes and EIT light storage, which is due to the spatially retarded coherence phases after EIT light storage. Similar behavior is also expected for other light-storage protocols with spatial retardation or for rephasing of collective quantum states with an unknown or undefined phase, e.g., as relevant in single-photon storage. We confirm the predictions of our theoretical model by experiments in a Pr$^{3+}$:Y$_{2}$SiO$_{5}$ crystal.

Decoherence of macroscopic objects from relativistic effect**Project supported by the National Natural Science Foundation of China (Grant Nos. 11421063 and 11534002), the National Key Basic Research Program of China (Grant No. 2014CB921403), the National Key Research and Development Program of China (Grant No. 2016YFA0301201), and the NSAF (Grant No. U1530401).

We study how the decoherence of macroscopic objects originates intrinsically from the relativistic effect. With the degree of freedom of the center of mass (CM) characterizing the collective quantum state of a macroscopic object (MO), it is found that an MO consisting of N particles can decohere with a time scale of no more than . Here, the special relativity can induce the coupling of the collective motion mode and the relative motion modes in an order of 1/c2, which intrinsically results in the above minimum decoherence.

Multiharmonic Frequency-Chirped Transducers for Surface-Acoustic-Wave Optomechanics

Wide passband interdigital transducers are employed to establish a stable phase-lock between a train of laser pulses emitted by a mode-locked laser and a surface acoustic wave generated electrically by the transducer. The transducer design is based on a multi-harmonic split-finger architecture for the excitation of a fundamental surface acoustic wave and a discrete number of its overtones. Simply by introducing a variation of the transducer's periodicity $p$, a frequency chirp is added. This combination results in wide frequency bands for each harmonic. The transducer's conversion efficiency from the electrical to the acoustic domain was characterized optomechanically using single quantum dots acting as nanoscale pressure sensors. The ability to generate surface acoustic waves over a wide band of frequencies enables advanced acousto-optic spectroscopy using mode-locked lasers with fixed repetition rate. Stable phase-locking between the electrically generated acoustic wave and the train of laser pulses was confirmed by performing stroboscopic spectroscopy on a single quantum dot at a frequency of 320 MHz. Finally, the dynamic spectral modulation of the quantum dot was directly monitored in the time domain combining stable phase-locked optical excitation and time-correlated single photon counting. The demonstrated scheme will be particularly useful for the experimental implementation of surface acoustic wave-driven quantum gates of optically addressable qubits or collective quantum states or for multi-component Fourier synthesis of tailored nanomechanical waveforms.

The magnon BEC observation by switch off method

The Bose–Einstein condensation (BEC) corresponds to the formation of a collective quantum state in which macroscopic number of particles is governed by a single wave function. The magnon BEC forms by excited non-equilibrium magnons and manifests itself by coherent precession of magnetization even in an inhomogeneous magnetic field. The magnon BEC is very similar to an atomic BEC, but the potential of the interaction between magnons may variate very significantly. The superfluid phases of 3He are the best antiferromagnetic system for investigations of magnon BEC and spin superfluidity. The 6 different states of magon BEC were observed in 3He. Recently magnon BEC was observed in antiferromagnets with Suhl–Nakamura interaction and ferrites. Here we review for the first time the switch off NMR method, when magnon BEC forms during a long radiofrequency pulse. The new experimental results are discussed.

Nonequilibrium-induced enhancement of dynamical quantum coherence and entanglement of spin arrays

The random magnetic field produced by nuclear spins has long been viewed as the dominating source of decoherence in the quantum-dot based spins. Here we obtain in both exact and analytical manner the dynamics of spin qubits coupled to nuclear spin environments via the hyperfine interaction, going beyond the weak system-bath interaction and Markovian approximation. We predict that the detailed-balance breaking produced by chemical potential gradient in nuclear baths leads to the rapid oscillations of populations, quantum coherence and entanglement, which are absent in the conventional case (i.e., Overhauser noise). This is attributed to the nonequilibrium feature of the system as shown in the relation between the oscillation period and the chemical potential imbalance. Our results reveal the essentiality of nonequilibriumness with detailed-balance breaking for enhancing the dynamical coherence and entanglement of spin qubits. Moreover, our exact solution explicitly demonstrates that the non-Markovian bath comprised by nuclear spins can preserve the collective quantum state, due to the recovery of coherence. Finally, we propose an experiment using ultracold trapped ions to observe these nonequilibrium and memory effects.