Driving Field Strength Research Articles

Emergent patterns in shape-asymmetric Quincke rollers

This study investigates the Quincke rolling phenomenon of snowman-shaped colloidal particles. These chiral rollers exhibit individual and collective dynamic states that depend upon the population and driving field strength. In addition to the previously identified dynamic states, such as spinning and vortex states, we identify the standing and bounded motion of the particles. The bounded motion involves the confined orbiting of particles around the center of mass due to hydrodynamic interactions at low particle area fractions. Our findings provide valuable insights into the behavior of active systems and the fabrication of active materials, emphasizing emergent order and adaptability as key guiding principles.

Heating of Large Endovascular Stents and Stent Grafts in Magnetic Particle Imaging—Influence of Measurement Parameters and Isocenter Distance

PurposeMagnetic particle imaging (MPI) is a tomographic imaging modality with the potential for cardiovascular applications. In this context, the extent to which stents are heated should be estimated from safety perspective. Furthermore, the influence of the measurement parameters and stent distance to the isocenter of the MPI scanner on stent heating were evaluated.Materials and MethodsNine different endovascular stents and stent grafts were tested in polyvinyl-chloride tubes. The stents had diameters from 10 to 31 mm, lengths between 25 and 100 mm and were made from stainless steel, nitinol or cobalt-chromium. The temperature differences were recorded with fiber-optic thermometers. All measurements were performed in a preclinical commercial MPI scanner. The measurement parameters were varied (drive field strengths: 3, 6, 9, 12 mT and selection field gradients: 0, 1.25 and 2.5 T/m). Furthermore, measurements with different distances to the scanner’s isocenter were performed (100 to 0 mm).ResultsAll stents showed heating (maximum 53.1 K, minimum 4.6 K). The stent diameter directly correlated with the temperature increase. The drive field strength influenced the heating of the stents, whereas the selection field gradient had no detectable impact. The heating of the stents decreased with increasing distance from the scanner’s isocenter and thus correlated with the loss of the scanner’s magnetic field.ConclusionStents can cause potentially harmful heating in MPI. In addition to the stent diameter and design, the drive field strength and the distance to the MPI scanner’s isocenter must be kept in mind as influencing parameters.

Nonequilibrium phase transition in a driven-dissipative quantum antiferromagnet

A deeper theoretical understanding of driven-dissipative interacting systems and their nonequilibrium phase transitions is essential both to advance our fundamental physics understanding and to harness technological opportunities arising from optically controlled quantum many-body states. This paper provides a numerical study of dynamical phases and the transitions between them in the nonequilibrium steady state of the prototypical two-dimensional Heisenberg antiferromagnet with drive and dissipation. We demonstrate a nonthermal transition that is characterized by a qualitative change in the magnon distribution, from subthermal at low drive to a generalized Bose-Einstein form including a nonvanishing condensate fraction at high drive. A finite-size analysis reveals static and dynamical critical scaling at the transition, with a discontinuous slope of the magnon number versus driving field strength and critical slowing down at the transition point. Implications for experiments on quantum materials and polariton condensates are discussed.

Quantum information processing with nuclear spins mediated by a weak-mechanically controlled electron spin

We propose a scheme to achieve nuclear–nuclear indirect interactions mediated by a mechanically driven nitrogen-vacancy (NV) center in a diamond. Here we demonstrate two-qubit entangling gates and quantum-state transfer between two carbon nuclei. When the dipole–dipole interaction strength is much larger than the driving field strength, the scheme is robust against decoherence caused by coupling between the NV center (nuclear spins) and the environment. Conveniently, precise control of dipole coupling is not required so this scheme is insensitive to fluctuating positions of the nuclear spins and the NV center. Our scheme provides a general blueprint for multi-nuclear-spin gates and for multi-party communication.

Fast generation of cat states in Kerr nonlinear resonators via optimal adiabatic control

Macroscopic cat states have been widely studied to illustrate fundamental principles of quantum physics as well as their applications in quantum information processing. In this paper, we propose a quantum speed-up method for the creation of cat states in a Kerr nonlinear resonator (KNR) via optimal adiabatic control. By simultaneously adiabatic tuning the cavity-field detuning and driving field strength, the width of the minimum energy gap between the target trajectory and non-adiabatic trajectory can be widened, which allows us to accelerate the evolution along the adiabatic path. Compared with the previous proposal, preparing cat states only by controlling two-photon pumping strength, our method can prepare the target state with a shorter time, a high-fidelity and a large non-classical volume. It is worth noting that the cat state prepared here is also robust against single-photon loss. Moreover, when we consider the KNR with a large initial detuning, our proposal will create a large-size cat state successfully. This proposal for preparing cat states can be implemented in superconducting quantum circuits, which provides a quantum state resource for quantum information encoding and fault-tolerant quantum computing.

DC current generation and power feature in strongly driven Floquet-Bloch systems

We study the DC current generation in a periodically driven Bloch system connected to a heat bath. Under a relaxation time approximation, the density matrix for such a system is obtained, which is related to two equilibria: a Floquet quasiequilibrium where the density matrix is diagonal under the Floquet-Bloch eigenbasis and an instantaneous Bloch thermal equilibrium. Then, the current responses and their power features, i.e., the power input behavior, are discussed in a unified manner, which reveals that there exist an intrinsic current and an extrinsic correction. Remarkably, the intrinsic part consumes no energy and corresponds to the Floquet quasiequilibrium, while the extrinsic part needs a sustained energy input and originates from a shift between two equilibrium ensembles. We further investigate the role of the external driving field strength finding that large DC currents can be generated under a relatively strong but not too strong driving field.

Semiclassical and quantum nonlinear spectra of a strongly coupled single Λ-type three-level atom-cavity QED system

We present detailed numerical simulations of semiclassical and quantum spectra of a cavity QED system consisting of a single three-level atom in Λ-configuration interacting with a quantized cavity mode through one of its transitions while its other transition is driven by a coherent classical field. We compute the semiclassical and quantum spectra of the system under various levels of external driving field strengths. In the semiclassical approach, we neglect the correlations between the cavity and atomic operators, whereas in the quantum case no such assumption is made. Our results show that the two approaches yield identical results under sufficiently weak driving field conditions. However, the two approaches yield starkly different results at stronger driving field intensities: the fully quantum approach yields a well-defined multiphoton spectrum whereas the semiclassical approach results in a bistable spectrum. Furthermore, our calculations reveal a complex Raman structure at the position of the dark-state transition.

Structure, dielectric, electrostrictive and electrocaloric properties of environmentally friendly Bi-substituted BCZT ferroelectric ceramics

In this study, environmentally friendly Bi-substituted [(Ba0.85Ca0.15)1-3x/2Bix](Zr0.1Ti0.9)O3 (BCZT-xBi) ferroelectric ceramics with x = 0–0.08 were prepared using a solid-state sintering method. The structures, dielectric, electrostrictive and electrocaloric properties of the Bi-substituted BCZT ceramics were thoroughly investigated. With an increase in the Bi3+ content, the temperature corresponding to the maximum permittivity (Tm) decreased monotonously. Meanwhile, the broadening of the dielectric peaks and the increase in the relaxation coefficient of the ceramics transformed their typical ferroelectric-to-paraelectric phase transition to diffuse phase transition (DPT). This was further confirmed by the trends shown by the ferroelectric properties of the ceramics. The current peak intensity in current-electric field (I-E) curves decreased with an increase in x and finally became constant, indicating that domain reversal disappeared gradually. High electrostrictive coefficient Q33 values of 0.0307, 0.0299 and 0.0223 m4/C2 were obtained for the ceramics with x = 0.02, 0.04 and 0.06 respectively. The Q33 values of the ceramics indicated their temperature-insensitive nature over the temperature range of 30–120 °C. Although the maximum value of the electrocaloric adiabatic temperature change (ΔT) (0.91 K) was achieved at x = 0.02, the thermally stability of ΔT is improved with an increase in x from 0.02 to 0.06. The results indicated that x = 0.06 improved the thermal stability of the electrostrictive and electrocaloric performance. By increasing the driving field strength, better electrostrictive and electrocaloric responses could be achieved.

Observing light-induced Floquet band gaps in the longitudinal conductivity of graphene

Floquet engineering presents a versatile method of dynamically controlling material properties. The light-induced Floquet-Bloch bands of graphene feature band gaps, which have not yet been observed directly. We propose optical longitudinal conductivity as a realistic observable to detect light-induced Floquet band gaps in graphene. These gaps manifest as resonant features in the conductivity, when resolved with respect to the probing frequency and the driving field strength. The electron distribution follows the light-induced Floquet-Bloch bands, resulting in a natural interpretation as occupations of these bands. Furthermore, we show that there are population inversions of the Floquet-Bloch bands at the band gaps for sufficiently strong driving field strengths. This strongly reduces the conductivity at the corresponding frequencies. Therefore our proposal puts forth not only an unambiguous demonstration of light-induced Floquet-Bloch bands, which advances the field of Floquet engineering in solids, but also points out the control of transport properties via light, that derives from the electron distribution on these bands.

Adiabaticity parameters for the categorization of light-matter interaction: From weak to strong driving

We investigate theoretically and numerically the light-matter interaction in a two-band system (TBS) as a model system for excitation in a solid-state band structure. We identify five clearly distinct excitation regimes, categorized with well-known adiabaticity parameters: (1) the perturbative multiphoton absorption regime for small driving field strengths, and four light-field-driven regimes, where intraband motion becomes important (2) the impulsive Landau-Zener (LZ) regime, (3) the nonimpulsive LZ regime, (4) the adiabatic regime, and (5) the adiabatic-impulsive regime for large electric field strengths. This categorization is tremendously helpful to understand the highly complex excitation dynamics in solids, in particular, when the driving field strength varies, and this categorization naturally connects Rabi physics with Landau-Zener physics. In addition, we find an insightful analytical expression for the photon orders connecting the perturbative multiphoton regime with the light-field-driven regimes. Moreover, in the adiabatic-impulsive regime, adiabatic motion and impulsive LZ transitions are equally important, leading to a broken symmetry of the TBS and a residual current when applying few-cycle laser pulses of broken temporal symmetry. This categorization allows a deep understanding of strong-field excitation in solids, including current and high-harmonic generation in a large variety of settings, and will help to find optimal driving parameters for a given purpose.

Crosstalk analysis for single-qubit and two-qubit gates in spin qubit arrays

Scaling up spin qubit systems requires high-fidelity single-qubit and two-qubit gates. Gate fidelities exceeding $98%$ were already demonstrated in silicon-based single and double quantum dots, whereas for the realization of larger qubit arrays, crosstalk effects on neighboring qubits must be taken into account. We analyze qubit fidelities impacted by crosstalk when performing single-qubit and two-qubit operations on neighbor qubits with a simple Heisenberg model. Furthermore, we propose conditions for driving fields to robustly synchronize Rabi oscillations and avoid crosstalk effects. In our analysis, we also consider crosstalk with two neighbors and show that double synchronization leads to a restricted choice for the driving field strength, exchange interaction, and thus gate time. Considering realistic experimental conditions, we propose a set of parameter values to perform a nearly crosstalk-free cnot gate and so open up the pathway to scalable quantum computing devices.

Optomechanically Induced Transparency and Slow–Fast Light Effect in Hybrid Cavity Optomechanical Systems

We theoretically investigate the optomechanically induced transparency (OMIT) phenomenon and the fast and slow light effects of a four-mode optomechanical system with the Kerr medium. The optomechanical system is composed of an array of three single-mode cavities and a mechanical oscillator. The three cavities are a passive cavity, a no-loss-gain cavity and a gain optical cavity, respectively. A Kerr medium is inserted in the passive cavity. We study the influence of the Kerr medium on the stability of the optomechanical system, and find that the stable regime of the optomechanical system can be adjusted by changing the Kerr coefficient. We demonstrate that the phenomenon of optomechanically induced transparency will appear when the Kerr medium exists in the optomechanical system and find that the frequency position of the absorption peak on the left increases linearly with the Kerr coefficient. In addition, we also investigate the fast and slow light effects in this system. The results show that we can control the fast and slow light by adjusting the Kerr coefficient, tunneling strength, and driving field strength. This study has potential application prospects in the fields of quantum optical devices and quantum information processing.

Measuring the Magnetic Field Amplitude of rf Radiation by the Quasistatic Magnetic Field Effect in Organic Light-Emitting Diodes

Electron paramagnetic resonance (EPR) is a versatile tool to probe spin physics in organic semiconductor materials. A common method used to detect the spin-\textonehalf{} paramagnetic resonance in organic light-emitting diodes (OLEDs) is to measure the device resistance under EPR conditions, i.e., to record electrically detected magnetic resonance (EDMR). Here, we present ultralow-frequency EDMR experiments on OLEDs that exhibit a qualitatively new line shape because of a quasistatic magnetic field effect: the modulation of the static ultrasmall field-effect magnetoresistance arising from the magnetic field amplitude ${B}_{1}$ of the radio frequency (rf) radiation. The disappearance of spin-\textonehalf{} Zeeman resonances of individual charge carriers in the OLED, i.e., the resonances at magnetic fields where the Zeeman splitting matches the photon energy of the incident rf radiation, coincides with the emergence of the quasistatic effect. We discuss the origin of this quasistatic magnetic field effect, its characteristic line shape in terms of the magnetic field dependence, the influence of experimental parameters, and the application potential with regards to EDMR experiments. The EDMR line shape can be inferred numerically from the magnetoresistance measurements. This approach enables a unique means of determining the drive-field strength ${B}_{1}$ in EDMR under driving conditions where alternative methods employing an analysis of the Zeeman resonance---such as power broadening and Rabi flopping---are not applicable.

Floquet states in dissipative open quantum systems

We theoretically investigate basic properties of nonequilibrium steady states of periodically-driven open quantum systems based on the full solution of the Maxwell–Bloch equation. In a resonant driving condition, we find that the transverse relaxation, also known as decoherence, significantly destructs the formation of Floquet states while the longitudinal relaxation does not directly affect it. Furthermore, by evaluating the quasienergy spectrum of the nonequilibrium steady states, we demonstrate that Rabi splitting can be observed as long as the decoherence time is as short as one third of the Rabi-cycle. Moreover, we find that Floquet states can be formed even under significant dissipation when the decoherence time is substantially shorter than the cycle of driving, once the driving field strength becomes strong enough. In an off-resonant condition, we demonstrate that the Floquet states can be realized even in weak field regimes because the system is not excited and the decoherence mechanism is not activated. Once the field strength becomes strong enough, the system can be excited by multi-photon absorption and the decoherence process becomes active. As a result, the Floquet states are significantly disturbed by the environment even in the off-resonant condition. Thus, we show here that the suppression of energy transfer from light to matter is a key condition for the realization of Floquet states in both on- and off-resonant conditions not only because it prevents material damage but also because it contributes to preserving coherence.

Multiplicative suppression of decoherence.

Combining different protocols extends the life of a quantum system

Adiabatic Fock-state-generation scheme using Kerr nonlinearity

We propose a theoretical scheme to deterministically generate Fock states in a Kerr cavity thorough adiabatic variation of the driving field strength and the cavity detuning. We show that the required time to generate a $n$-photon Fock state scales as the square root of $n$. Requirements for the Kerr coefficient relative to the system decoherence rate are provided as a function of desired state fidelity, indicating that the scheme is potentially realizable with the present state of the art in microwave superconducting circuits.

Output field squeezing in a weakly-driven dissipative quantum Rabi model

Abstract We present a generalized method to address the squeezing spectrum of the output field for a weakly-driven, dissipative quantum Rabi model and calculate it for a range of coupling strengths covering strong, ultra-strong and deep-strong coupling regimes. The need for a generalization arises because of the periodic time dependence of the correlation functions due to counter rotating terms in the quantum Rabi model. We here adopt time-averaging over such correlation functions to obtain the squeezing spectrum, which may also be relevant to experimental situations. We compare the calculated squeezing spectra with those of the driven dissipative Jaynes–Cummings model to illustrate the departure from the latter as the interaction strength increases. Our calculation shows that the overall squeezing increases with the interaction strength after optimization over the system-bath coupling strength and the driving field strength.

Modulating the single-photon transport periodically with two emitters in two one-dimensional coupled cavity arrays

Abstract We theoretically investigate the coherent transport behavior of a single-photon in T-type coupled cavity arrays (CCAs). Firstly, the case two two-level atoms (TLA) located inside two cavities of the incident channel is investigated, with the first TLA fixed at the T node and the second TLA in any position of CCA-a. The results show that the position of the second atom can periodically manipulate the transfer rate, and the single-photon can be completely routed into CCA-b deterministically. Secondly, we consider the two Λ -type three level atom instead of the two-level atom. When the driving field is present, the Fano-resonance can be observed and gradually becomes a double-peak with the increase of the driving field strength. In addition, the Rabi frequency of the first atom can alter the position of the double-peak, while the driving field intensity of the second atom only varies the peak value of the transfer rate, and the maximum probability may be obtained when the Rabi frequencies of the two Λ -type TLA are equal.

Quantitative measurements of dielectrophoresis in a nanoscale electrode array with an atomic force microscopy.

Nanoelectronic devices integrated with dielectrophoresis (DEP) have been promoted as promising platforms for trapping, separating, and concentrating target biomarkers and cancer cells from a complex medium. Here, we visualized DEP and DEP gradients in conventional nanoelectronic devices by using multi-pass atomic force microcopy techniques. Our measurements directly demonstrated a short range DEP only at sharp step edges of electrodes, frequency dependent DEP polarity, and separation distance dependent DEP strength. Additionally, non-uniform DEP along the edges of the electrodes due to a large variation in electric field strength was observed. The strength and apparent working distance of DEP were measured to be an order of a few nN and 80 nm within the limited scale of particles and other parameters such as an ionic strength of the medium. This method provides a powerful tool to quantify the strength and polarity of DEP and allows optimizing and calibrating the device's operating parameters including the driving field strength for the effective control and manipulation of target biomolecules.

Nonlinear dynamics of a two-level system of a single spin driven beyond the rotating-wave approximation

Quantum systems driven by strong oscillating fields are the source of many interesting physical phenomena. In this work, we experimentally study the dynamics of a two-level system of a single spin driven in the strong-driving regime where the rotating-wave approximation is not valid. This two-level system is a subsystem of a single Nitrogen-Vacancy center coupled to a first-shell $^{13}$C nuclear spin in diamond at a level anti-crossing point that occurs in the $m_{s}=\pm1$ manifold when the energy level splitting between the $m_{s}$ = $+1$ and $-1$ spin states due to the static magnetic field is $\approx$ 127 MHz, which is roughly equal to the spectral splitting due to the $^{13}$C hyperfine interaction. The transition frequency of this electron spin two-level system in a static magnetic field of 28.9 G is 1.7 MHz and it can be driven only by the $z$-component of the RF field. Electron spin Rabi frequencies in this system can reach tens of MHz even for moderate RF powers. The simple sinusoidal Rabi oscillations that occur when the amplitude of the driving field is much smaller than the transition frequency become complex when the driving field strength is comparable or greater than the energy level splitting. We observe that the system oscillates faster than the amplitude of the driving field and the response of the system shows multiple frequencies.