Phase Relaxation Processes Research Articles

Dielectric relaxation studies in Sm2O3 doped boro-zinc-vanadate glasses

In this work, the conventional melting procedure was adopted to synthesize glasses with a composition of (ZnO)0.3 – (V2O5)0.3 – (B2O3)0.4-x – (Sm2O3)x, x = 0.002, 0.005, 0.007, 0.01 and 0.02 mol%. The dielectric properties of these glasses were measured. The dielectric constant (εʹ) and dielectric loss (εʹʹ) of glasses are found to vary in the range from 1.9177x102 to 3.9456x103 and from 1.5751 to 6.9095x105 respectively for the temperature range 343 K – 573 K and frequency range 50 Hz to 10 MHz. With increase of frequency, both dielectric constant and loss decreased and increased with increase of temperature. The analysis of dielectric constant and dielectric loss confirmed that the phenomenon of dielectric relaxation is mainly due to the frequency-dependent polarization mechanism. Electric modulus and impedence spectroscopy revealed non-Debye type and a single phase relaxation process. Activation energy for dc conductivity and dielectric relaxation are found to be of same size indicating that the potential barrier encountered by the charge carriers is same in both the processes. The master curves suggested that temperature-independent relaxation is occurring in the present glasses. The high values of measured dielectric parameters suggest that the present glasses are suitable in semiconducting and energy storage applications.

Investigation of relaxation processes and phase transitions in the silica gel-undecylenic acid system using IR spectra in a wide temperature range

The study of relaxation processes in porous inhomogeneous systems via dielectric and mechanical spectroscopy methods is associated with methodological difficulties. To understand how IR spectroscopy can be used to elucidate the temperature-dependent changes that take place in the undecylenic acid - porous silica gel systems, such as phase transition and relaxation processes, we compare IR spectroscopic data with previously obtained dielectric spectroscopy data for the bulk undecylenic acid and undecylenic acid embedded in silica gel matrices of different pore sizes. We demonstrate that the topological soliton model can be used for both bulk undecylenic acid, and the undecylenic acid in nanoporous silica gel matrices.

Octahedral distortion-driven phase transition, relaxation and conduction process of Zr/Sn modified barium titanate relaxors

This paper mainly reports the effect of Zr/Sn substitution on structural, dielectric, and electrical characteristics of pure BaTiO3 (BT). The addition of Zr4+ and Sn4+ at the Ti-site of BT has bas created compositional disordered state. The disordered state is the necessary/prerequisite for the development of the relaxor ferroelectrics. The appearance of polar nano-regions is the cause of the relaxor property of the ferroelectric. The dielectric characteristics of Ba(ZrTi)O3 (BZT) and Ba(SrTi)O3 (BST) deviate from those of traditional Curie Weiss law, and hence do not show a sharp phase transition, but little diffused as compared to that of BT. Impedance spectra is fitted to the modified Cole-Cole equation to reveal the (i) asymmetry and broadening of the dielectric/impedance dispersion curves, (ii) non-Debye type of relaxation, (iii) actual grain and grain boundary contributions and (iv) semiconductor or positive temperature coefficient of resistance (PTCR) nature of the prepared materials. The correlated barrier hopping model fits well to BT and BST, whereas overlapping polaron tunnelling and small polaron tunnelling models signify the conduction mechanism of BZT. Zr and Sn addition increases impedance, energy storage and decreases the conductivity, leakage current and loss energy of BT. The high energy efficiency, good temperature stability of energy efficiency, high recoverable energy density and high breakdown strength of BZT and BST is observed as compared to those of BT which satisfy their the energy storage applications. The relaxation phenomena and the connection of microscopic electrical grain and grain boundary with microstructure are discussed here.

Proposal for a solid-state magnetoresistive Larmor quantum clock

We propose a solid-state implementation of the Larmor clock that exploits tunnel magnetoresistance to distill information on how long itinerant spins take to traverse a barrier embedded in it. Keeping in mind that the tunnelling time innately involves pristine pre-selection and post-selection, our proposal takes into account the detrimental aspects of multiple reflections by incorporating multiple contacts, multiple current measurements and suitably defined magnetoresistance signals. Our analysis provides a direct mapping between the magnetoresistance signals and the tunneling times and aligns well with the interpretation in terms of generalized quantum measurements and quantum weak values. By means of an engineered pre-selection in one of the ferromagnetic contacts, we also elucidate how one can make the measurement "weak" by minimizing the back-action, while keeping the tunneling time unchanged. We then analyze the resulting interpretations of the tunneling time and the measurement back action in the presence of phase breaking effects that are intrinsic to solid state systems. We unravel that while the time-keeping aspect of the Larmor clock is reasonably undeterred due to momentum and phase relaxation processes, it degrades significantly in the presence of spin-dephasing. We believe that the ideas presented here also open up a fructuous solid state platform to encompass emerging ideas in quantum technology such as quantum weak values and its applications, that are currently exclusive to quantum optics and cold atoms.

Nonlinear Hall effect induced by internal Coulomb interaction and phase relaxation process in a four-terminal system with time-reversal symmetry

We numerically investigate the second-order nonlinear Hall transport properties of a four-terminal system with time-reversal symmetry and broken inversion symmetry. Within the nonequilibrium Green's function formalism, the second-order nonlinear conductances are derived, where the internal Coulomb potential in response to external voltages is explicitly included to guarantee the gauge invariance. For the system with single mirror symmetry ${\mathcal{M}}_{x}$, nonlinear Hall properties are only observable in the $y$ direction and contributed solely from the second-order nonlinear effect. From the symmetry point of view, the observed nonlinear Hall transport phenomena have one-to-one correspondence with the Berry curvature dipole induced nonlinear Hall effect semiclassically obtained for the same Hamiltonian. In addition to the nonlinear Hall effect originated from symmetries of the system, it is found that the internal Coulomb potential has the same symmetry of the four-terminal system, which gives rise to an extra nonlinear Hall response. Moveover, the phase relaxation mechanism modeled by virtual probes leads to the dephasing-induced nonlinear Hall effect.

Relaxing under pressure with a rigid niccolite formate framework

Order-disorder phase transition and relaxation process in lead free rigid niccolite-type formate crystal under pressure supported by the molecular dynamics simulations.

Quantum interference transport in AuGe alloy thin films

By using electron beam evaporation method, we have fabricated three AuGe ultrathin films with thickness of 8 nm, 11 nm and 15 nm respectively. The low temperature magnetoresistances of these films were measured. A sharply dip in the low-field magnetoresistance curves was observed in the AuGe films, which was associated to the weak anti-localization effect. Comparing our experimental results with theoretical predictions, we have extracted the temperature dependence of phase relaxation length Lϕ(T), which meets to the scaling law of Lϕ∝1/T. This observation certificated that the electron-phonon interaction plays a dominant role in the electron phase relaxation processes of AuGe films.

Quantum interference in the presence of a resonant medium

Interaction of light with media often occurs with a femtosecond response time. Its measurement by conventional techniques requires the use of femtosecond lasers and sophisticated time-gated optical detection. Here we demonstrate that by exploiting quantum interference of entangled photons it is possible to measure the dephasing time of a resonant media on the femtosecond time scale (down to 100 fs) using accessible continuous wave laser and single-photon counting. We insert a sample in the Hong-Ou-Mandel interferometer and observe the modification of the two-photon interference pattern, which is driven by the coherent response of the medium, determined by the dephasing time. The dephasing time is then inferred from the observed pattern. This effect is distinctively different from the basic effect of spectral filtering, which was studied in earlier works. In addition to its ease of use, our technique does not require compensation of group velocity dispersion and does not induce photo-damage of the samples. Our technique will be useful for characterization of ultrafast phase relaxation processes in material science, chemistry, and biology.

Phase Transitions and Relaxation Behaviors in Barium Strontium Titanate Ceramics Determined by Dynamic Mechanical and Dielectric Analysis

Barium strontium titanate (Ba1-xSrxTiO3) ceramics were prepared by solid-state reaction method. XRD patterns showed that BT (x = 0) and BST2 (x = 0.2) ceramics presented tetragonal phase, while BST4 (0.4) and BST6 (0.6) ceramics showed cubic phase at room temperature. The relative permittivity and dissipation factor of Ba1-xSrxTiO3 ceramics with temperature of 125–425 K were characterized at 1–100 kHz by LCR meter. The Young's modulus and internal friction of Ba1-xSrxTiO3 ceramics in the range of 125 K–425 K at different vibration frequencies were tested by a Dynamic Mechanical Analysis (DMA) system. Compared with the dielectric measurement, mechanical analysis was more sensitive to reflect the phase transition and relaxation process. All Ba1-xSrxTiO3 samples showed three phase transitions, the transition temperatures decreased and the phase transition diffused as Sr content increased. Besides, a relaxation process caused by the interaction between domain walls and lattice defects emerged in pure BT ceramic, while it disappeared in all BST ceramics.

Photoluminescence of a quantum-dot molecule

The coherent coupling of quantum dots is a sensitive indicator of the energy and phase relaxation processes taking place in the nanostructure components. We formulate a theory of low-temperature, stationary photoluminescence from a quantum-dot molecule composed of two spherical quantum dots whose electronic subsystems are resonantly coupled via the Coulomb interaction. We show that the coupling leads to the hybridization of the first excited states of the quantum dots, manifesting itself as a pair of photoluminescence peaks with intensities and spectral positions strongly dependent on the geometric, material, and relaxation parameters of the quantum-dot molecule. These parameters are explicitly contained in the analytical expression for the photoluminescence differential cross section derived in the paper. The developed theory and expression obtained are essential in interpreting and analyzing spectroscopic data on the secondary emission of coherently coupled quantum systems.

Polarization effect for dielectric and mechanical behaviors in Pb(Mg1/3,Nb2/3)0.71Ti0.29O3 crystal

The relative permittivity and dissipation factor of (001)-cut Pb(Mg1/3Nb2/3)0.71Ti0.29O3 (PMNT29%) single crystal as functions of temperature were characterized at different frequencies by a LCR meter. From 280K to 480K, the unpoled sample showed three phase transitions: rhombohedral→tetragonal macro-domain→tetragonal micro-domain→cubic. The <001>-poled sample showed electric-field-induced monoclinic symmetry at room temperature, and also exhibited three phase transitions from 280K to 480K: monoclinic→tetragonal macro-domain→tetragonal micro-domain→cubic. The Young’s modulus and internal friction of PMNT29% crystal as functions of temperature at different vibration frequencies were tested by a dynamic mechanical analysis (DMA) system. Compared with the dielectric measurement during the phase transitions, mechanical measurement was more sensitive to reflecting the phase transition and relaxation process. On average, the Young’s modulus of the poled sample was 15% higher than that of unpoled sample, which is probably due to the changes of structure and internal stress induced by polling. Besides, a relaxation process caused by the interaction between domain walls and lattice defects emerged in the unpoled sample, while it disappeared in the poled sample due to the enhanced long-range domain order by field-induced phase transition.

Coherent control of a classical nanomechanical two-level system

The Bloch sphere is a generic picture describing a coupled two-level system and the coherent dynamics of its superposition states under control of electromagnetic fields. It is commonly employed to visualise a broad variety of phenomena ranging from spin ensembles and atoms to quantum dots and superconducting circuits. The underlying Bloch equations describe the state evolution of the two-level system and allow characterising both energy and phase relaxation processes in a simple yet powerful manner. Here we demonstrate the realisation of a nanomechanical two-level system which is driven by radio frequency signals. It allows to extend the above Bloch sphere formalism to nanoelectromechanical systems. Our realisation is based on the two orthogonal fundamental flexural modes of a high quality factor nanostring resonator which are strongly coupled by a dielectric gradient field. Full Bloch sphere control is demonstrated via Rabi, Ramsey and Hahn echo experiments. This allows manipulating the classical superposition state of the coupled modes in amplitude and phase and enables deep insight into the decoherence mechanisms of nanomechanical systems. We have determined the energy relaxation time T1 and phase relaxation times T2 and T2*, and find them all to be equal. This not only indicates that energy relaxation is the dominating source of decoherence, but also demonstrates that reversible dephasing processes are negligible in such collective mechanical modes. We thus conclude that not only T1 but also T2 can be increased by engineering larger mechanical quality factors. After a series of ground-breaking experiments on ground state cooling and non-classical signatures of nanomechanical resonators in recent years, this is of particular interest in the context of quantum information processing.

Heat capacity and electrical resistance of (PbySn1-y)2P2S6 chalcogenides

We present the results of study of heat capacity and electrical resistance of the (PbySn1-y)2P2S6 chalcogenides where Pb content varies from 0 till 0.8. We have studied the temperature behaviour of heat capacity from the point of Pb influence on change of transition temperature at the temperature region 50–400 K Moreover, we present the results of study of temperature dependence of electrical resistance and influence of an applied magnetic field up to 3 T The electrical resistance was studied in the temperature range 50–400 K due to low temperature semiconducting behaviour. We studied the influence of Pb content on phase transition and relaxation processes.

Quantum noise and the quality control of hardware components of quantum computers based on superconducting phase qubits

A general approach to the provision of the quality and efficiency of quantum information technologies is proposed. The approach is based on the analysis of quantum noise generated on the implementation of quantum operations. The method of precision quantum measurements of logic quantum gates based on superconducting phase qubits is developed. The universal method of quantum state and process tomography is used to carry out a comprehensive analysis of the fidelity of the tomography of two-qubit SQiSW, CNOT, and CZ gates arising from the capacitive coupling between qubits. The method of optimization of quantum process tomography is proposed to provide a substantially higher degree of adequacy and fidelity compared to those attained by previously known methods. The examples of simulation of depolarizing quantum noise and amplitude- and phase-relaxation processes on the implementation of quantum operations in registers are considered.

Conformational relaxation dynamics of a poly(N-isopropylacrylamide) aqueous solution measured using the laser temperature jump transient grating method

We observed phase transition and phase relaxation processes of a poly(N-isopropylacrylamide) (PNIPAM) aqueous solution using the heterodyne transient grating (HD-TG) method combined with the laser temperature jump technique. The sample temperature was instantaneously raised by about 1.0 K after irradiation of a pump pulse to crystal violet (CV) molecules for heating, and the phase transition was induced for the sample with an initial temperature just below the lower critical solution temperature (LCST); the following phase relaxation dynamics was observed. Turbidity relaxation was observed in both the turbidity and HD-TG responses, while another relaxation process was observed only in the HD-TG response, namely via the refractive index change. It is suggested that this response is due to formation of globule molecules or their assemblies since they would have nothing to do with turbidity change but would affect the refractive index, which is dependent on the molar volume of a chemical species. Furthermore, the grating spacing dependence of the HD-TG responses suggests that the response was caused by the counter propagating diffusion of the coil molecules as a reactant species and the globule molecules as a product species and the lifetime of the globule molecules ranged from 1.5 to 5 seconds. Thus, we conclude that the turbidity reflects the dynamics of aggregate conditions, not molecular conditions. The coil and globule sizes were estimated from the obtained diffusion coefficient. The sizes of the coil molecules did not change at the initial temperatures below the LCST but increased sharply as it approaches LCST. We propose that the coil-state molecules associate due to hydrophobic interaction when the initial temperature was higher than LCST minus 0.5 K and that the globule-state molecules generated from the coil-state molecules showed a similar trend in temperature. The phase transition was also induced by heating under a microscope, and the relaxation process was followed using the fluorescence peak shift of a fluorescent molecule-labeled PNIPAM. The result also supports the existence of a globule molecule or its assembly remains for several seconds in the phase relaxation.

Phase transition and relaxation processes by 87Rb and 39K nuclear magnetic measurements of RbKSO4 single crystals

Abstract 87 Rb and 39 K nuclear magnetic resonance (NMR) spectra of RbKSO 4 single crystals were measured at room temperature. 87 Rb central line has the angular dependences of second-order quadrupolar shifts. From these results, the quadrupole coupling constant and the asymmetry parameter were determined at room temperature. In addition, the spin–lattice relaxation rate, 1/ T 1 , and the spin–spin relaxation rate, 1/ T 2 , were measured as a function of temperature. The values of 1/ T 1 for the 87 Rb and 39 K nuclei were found to increase with increasing temperature, and 1/ T 1 was determined to be proportional to T n . Therefore, for the 87 Rb and 39 K nuclei, Raman processes with n =2 are more significantly in nuclear quadrupole relaxation than direct processes.

Non-Markovian dynamics of a damped driven two-state system

We study a driven two-state system interacting with a structured environment. We introduce the non-Markovian master equation ruling the system dynamics, and we derive its analytic solution for general reservoir spectra. We compare the non-Markovian dynamics of the Bloch vector for two classes of reservoir spectra: the Ohmic and the Lorentzian reservoir. Finally, we derive the analytic conditions for complete positivity with and without the secular approximation. Interestingly, the complete positivity conditions have a transparent physical interpretation in terms of the characteristic timescales of phase diffusion and relaxation processes.

Dephasing of two interacting qubits under the influence of thermal reservoirs

A phase relaxation process of interacting two qubits is studied by means of the quantum master equation, where each qubit is influenced by an independent thermal reservoir. The damping operator of the quantum master equation consists of two parts; one includes the effects of the interaction between the qubits and the other does not. It is shown that the interaction significantly affects the phase relaxation process. The decoherence of entanglement is investigated for the two qubits initially prepared in the $X$ state.

Study on structural phase transitions and relaxation processes of Cs 2Co(SO 4) 2·6H 2O and Cs 2Zn(SO 4) 2·6H 2O crystals

The structural phase transitions and relaxation processes of Cs 2Co(SO 4) 2·6H 2O and Cs 2Zn(SO 4) 2·6H 2O single crystals were investigated, with the phase transitions of both crystals being determined from NMR data. The spin–lattice relaxation time, T 1, of the 133Cs nucleus in two crystals undergoes a significant change near the phase transition temperature, T C, and these changes coincide with the changes in the splitting of the 133Cs resonance lines. The variations in the temperature dependence for the splitting of the 133Cs resonance lines and T 1 near T C are related to changes in the symmetry of surrounding Cs +. In addition, the 133Cs T 1 of Cs 2Co(SO 4) 2·6H 2O, which contains paramagnetic ions, was found to be shorter than that of Cs 2Zn(SO 4) 2·6H 2O. This relaxation time is inversely proportional to the square of the magnetic moment of the paramagnetic ions. The differences between the 133Cs T 1 of these compounds are probably due to the differences between the electronic structures of their metal ions.

Nonlinear optical properties and phase-relaxation processes in single-walled carbon nanotubes

We have investigated third-order nonlinear optical properties of bundled and isolated semiconducting single-walled carbon nanotubes (SWNTs) by means of Z-scan method, pump–probe method, and two-beam time-resolved degenerate four-wave mixing (DFWM) method. The figures of merit Im χ (3)/ α in both bundled and isolated SWNTs samples were found to be enhanced with increasing tube diameter. The measured Im χ (3)/ α value in the bundled SWNTs was an order of magnitude smaller than that in the isolated SWNTs. Both population relaxation time T 1 and phase-relaxation time T 2 for bundled samples were smaller than those in the isolated samples. These experimental results can be explained by an increase in nonradiative recombination rate and phase-relaxation rate in the bundled sample. The phase-relaxation time T 2 is considered to have a significant role in the enhancement of Im χ (3)/ α.