Triple Quantum Research Articles

Nonlinear dynamics of triple quantum dot molecules in a cavity: multi-stability of three types of cavity solitons

By numerical simulation of a cavity filled with triple quantum dot molecules under tunneling induced transparency, we show that various regimes of existence of different kinds of cavity solitons are possible. Forming in overlapping regions of a multistable parameter space, cavity solitons in this system exhibit different dynamical behaviors: stationary on a flat background when there is only one cavity soliton branch, oscillating when two cavity soliton branches coexist, and stationary-rambling on a honeycomb background arising from simultaneous presence of a stable pattern and a cavity soliton branch. In particular, we show that three different types of dissipative localized structures can be excited in multistable regions where material coherence is high due to light-matter interaction processes.

Charge qubit in a triple quantum dot with tunable coherence

The energy landscape of a single electron in a triple quantum dot can be tuned such that the energy separation between ground and excited states becomes a flat function of the relevant gate voltages. These so-called sweet spots are beneficial for charge coherence, since the decoherence effects caused by small fluctuations of gate voltages or surrounding charge fluctuators are minimized. We propose a new operation point for a triple quantum dot charge qubit, a so-called $CQ_3$-qubit, having a third order sweet spot. We show strong coupling of the qubit to single photons in a frequency tunable high-impedance SQUID-array resonator. In the dispersive regime we investigate the qubit linewidth in the vicinity of the proposed operating point. In contrast to the expectation for a higher order sweet spot, we there find a local maximum of the linewidth. We find that this is due to a non-negligible contribution of noise on the quadrupolar detuning axis not being in a sweet spot at the proposed operating point. While the original motivation to realize a low-decoherence charge qubit was not fulfilled, our analysis provides insights into charge decoherence mechanisms relevant also for other qubits.

Influence of Al/Er ratio on the optical properties and structures of Er3+/ Al3+ co-doped silica glasses

In this study, Er3+/Al3+ co-doped silica glasses with various Al/Er ratios ranging from 0 to 200 and a constant Er2O3 amount were prepared using the sol-gel method combined with high-temperature vacuum sintering. The absorption, emission spectra, and fluorescence lifetime of Er3+ ions were recorded and the absorption and emission cross sections were calculated. Using Raman, 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS-NMR), 27Al triple-quantum (TQ)-MAS-NMR, and electron paramagnetic resonance (EPR) spectroscopies, the physical and optical properties were correlated with the glass structural modifications due to the Al/Er ratio change. With the increase in the Al/Er ratio, the content of Al3+ ions around the Er3+ ions gradually increased. Meanwhile, the AlO5 and AlO6 polyhedrons increased at the expense of the AlO4 and SiO4 tetrahedrons, which resulted in an improved symmetry and better ionic Er–O bonds. These structural changes led to the site-to-site variations in the Er3+ local environment and the changes in the ligand field strength of the Er–O bonds. This, in turn, resulted in the inhomogeneous broadening of the absorption and emission spectra, with a blue shift of both absorption and emission peaks and a decrease in both absorption and emission at 1.53 μm. With the increase in Al/Er ratio, the full width at half maximum (FWHM) of the emission increased from 27.2 to 54.3 nm. The FWHM × emission cross section (σemi) parameter for evaluating broadband amplification behavior was 30.1 × 10−20 cm2 · nm. This work reveals the close relationship between the glass structure and the spectroscopic properties of Er3+ ions and provides an important reference for the design of broadband amplifier materials in the field of optical communication.

Realistic nonlocal refrigeration engine based on Coulomb-coupled systems.

We investigate, in detail, a triple quantum dot system that exploits Coulomb coupling to achieve nonlocal refrigeration. The system under investigation is a derivative of the nonlocal thermodynamic engine, originally proposed by Sánchez and Büttiker [Phys. Rev. B 83, 085428 (2011)PRBMDO1098-012110.1103/PhysRevB.83.085428], that employs quadruple quantum dots to attain efficient nonlocal heat harvesting. Investigating the cooling performance and operating regime using the quantum master equation approach, we point out some crucial aspects of the refrigeration engine. In particular, we demonstrate that the maximum cooling power for the setup is limited to about 70% of the optimal design. Proceeding further, we point out that to achieve a target reservoir temperature lower than the average temperature of the current path, the applied voltage must be greater than a given threshold voltage V_{TH} that increases with the decrease in the target reservoir temperature. In addition, we demonstrate that the maximum cooling power, as well as the coefficient of performance, deteriorates as one approaches a lower target reservoir temperature. The triple quantum dot system, investigated in this paper, combines fabrication simplicity along with descent cooling power and may pave the way towards the practical realization of efficient nonlocal cryogenic refrigeration systems.

Effect of position-dependent effective mass on electron tunneling of InAs/GaSb type-II superlattice having triangular and parabolic geometries

In a recent paper, we presented transmission probability of a triple quantum well triple barrier structure having triangular and parabolic geometries in presence of finite thick contact barriers using propagation matrix method for InAs/GaSb type-II superlattice. In this letter, effect of different barriers and wells widths and wells geometry are independently studied on transmission coefficient, and also for a specified structure, material composition of barriers is varied to observe the tunnelling effect. We show that the number of peaks in transmission (-ln(Trans(E))) for 30 nm wells width and 10 nm barriers width is more than10nm wells width and 30 nm barriers width.

Modulated longitudinal gates on encoded spin qubits via curvature couplings to a superconducting cavity

We propose entangling operations based on the energy curvature couplings of encoded spin qubits to a superconducting cavity, exploring the non-linear qubit response to a gate voltage variation. For a two-qubit ($n$-qubit) entangling gate we explore acquired geometric phases via a time-modulated longitudinal $\sigma_z$-coupling, offering gate times of 10s of ns even when the qubits and the cavity are far detuned. No dipole moment is necessary: the qubit transverse $\sigma_x$-coupling to the resonator is zero at the full sweet spot of the encoded spin qubit of interest (a triple quantum dot three-electron exchange-only qubit or a double quantum dot singlet-triplet qubit). This approach allows always-on, exchange-only qubits, for example, to stay on their "sweet spots" during gate operations, minimizing the charge noise and eliminating an always-on static longitudinal qubit-qubit coupling. We calculate the main gate errors due to the (1) diffusion (Johnson) noise and (2) damping of the resonator, the (3) $1/f$-charge noise qubit gate dephasing and $1/f$-noise on the longitudinal coupling, (4) qubit dephasing and ac-Stark frequency shifts via photon fluctuations in the resonator, and (5) spin-dependent resonator frequency shifts (via a "dispersive-like" static curvature coupling), most of them associated with the non-zero qubit energy curvature (quantum capacitance). Using spin-echo-like error suppression at optimal regimes, gate infidelities of $10^{-2}-10^{-3}$ can be achieved with experimentally existing parameters. The proposed schemes seem suitable for remote spin-to-spin entanglement of two spin-qubits or a cluster of spin-qubits: an important resource of quantum computing.

Detection of charge states of an InAs nanowire triple quantum dot with an integrated nanowire charge sensor

A linear triple quantum dot (TQD) integrated with a quantum dot (QD) charge sensor is realized. The TQD and the charge sensor are built from two adjacent InAs nanowires by the fine finger gate technique. The charge state configurations of the nanowire TQD are studied by measurements of the direct transport signals of the TQD and by detection of the charge state transitions in the TQD via the nanowire QD sensor. Excellent agreement in the charge stability diagrams of the TQD obtained by the direct transport measurements and by the charge-state transition detection measurements is achieved. It is shown that the charge stability diagrams are featured by three groups of charge state transition lines of different slopes, corresponding to the changes in the electron occupation numbers of the three individual QDs in the TQD. It is also shown that the integrated nanowire QD sensor is highly sensitive and can detect the charge state transitions in the cases where the direct transport signals of the TQD are too weak to be measurable. Tuning to a regime, where all three QDs in the TQD are close to being on resonance with the Fermi level of the source and drain reservoirs and co-existence of triple and quadruple points becomes possible, has also been demonstrated with the help of the charge sensor in the region where the direct transport signals of the TQD are hardly visible.

Off-target effects of sodium-glucose co-transporter 2 blockers: empagliflozin does not inhibit Na+/H+ exchanger-1 or lower [Na+]i in the heart.

Aims Emipagliflozin (EMPA) is a potent inhibitor of the renal sodium-glucose co-transporter 2 (SGLT2) and an effective treatment for type-2 diabetes. In patients with diabetes and heart failure, EMPA has cardioprotective effects independent of improved glycaemic control, despite SGLT2 not being expressed in the heart. A number of non-canonical mechanisms have been proposed to explain these cardiac effects, most notably an inhibitory action on cardiac Na+/H+ exchanger 1 (NHE1), causing a reduction in intracellular [Na+] ([Na+]i). However, at resting intracellular pH (pHi), NHE1 activity is very low and its pharmacological inhibition is not expected to meaningfully alter steady-state [Na+]i. We re-evaluate this putative EMPA target by measuring cardiac NHE1 activity.Methods and results The effect of EMPA on NHE1 activity was tested in isolated rat ventricular cardiomyocytes from measurements of pHi recovery following an ammonium pre-pulse manoeuvre, using cSNARF1 fluorescence imaging. Whereas 10 µM cariporide produced near-complete inhibition, there was no evidence for NHE1 inhibition with EMPA treatment (1, 3, 10, or 30 µM). Intracellular acidification by acetate-superfusion evoked NHE1 activity and raised [Na+]i, reported by sodium binding benzofuran isophthalate (SBFI) fluorescence, but EMPA did not ablate this rise. EMPA (10 µM) also had no significant effect on the rate of cytoplasmic [Na+]i rise upon superfusion of Na+-depleted cells with Na+-containing buffers. In Langendorff-perfused mouse, rat and guinea pig hearts, EMPA did not affect [Na+]i at baseline nor pHi recovery following acute acidosis, as measured by 23Na triple quantum filtered NMR and 31P NMR, respectively.Conclusions Our findings indicate that cardiac NHE1 activity is not inhibited by EMPA (or other SGLT2i’s) and EMPA has no effect on [Na+]i over a wide range of concentrations, including the therapeutic dose. Thus, the beneficial effects of SGLT2i’s in failing hearts should not be interpreted in terms of actions on myocardial NHE1 or intracellular [Na+].

Analysis of Triple Quantum Dots Single Electron Transistor (TQD-SET) for Various Configuration

<p class="Abstract">Single electron transistor (SET) has high potential for the development of quantum computing technologies in order to provide low power consumption electronics. For that purpose, many studies have been conducted to develop SET using dopants as quantum dots (QD). The working principle of SET basically is a single electron tunneling one by one through tunnel junction based on the coulomb blockade effect. This research will simulate various configurations of triple quantum dots single electron transistors (TQD-SET) using SIMON 2.0 with an experimental approach of MOSFET with dopants QD. The configurations used are series, parallel, and triangle configuration. The mutual capacitance (Cm), tunnel junctions (TJ), and temperature values of TQD-SET configurations are varied. The I-V characteristics are observed and analyzed for typical source-drain voltage (Vsd). it is found that the TQD series requires larger Vsd than parallel or triangular TQDs. On the other hands, the current in parallel TQD tends to be stable even though Cm is changed, and the current in the TQD triangle is strongly influenced by the Cm. By comparing these three configurations, it is observed that the tunnelling rate is higher for parallel TQD due to higher probability current moves through three dots by applying Vds.</p>

Quantitative 1H and 23Na muscle MRI in Facioscapulohumeral muscular dystrophy patients

ObjectiveOur aim was to assess the role of quantitative 1H and 23Na MRI methods in providing imaging biomarkers of disease activity and severity in patients with Facioscapulohumeral muscular dystrophy (FSHD).MethodsWe imaged the lower leg muscles of 19 FSHD patients and 12 controls with a multimodal MRI protocol to obtain STIR-T2w images, fat fraction (FF), water T2 (wT2), water T1 (wT1), tissue sodium concentration (TSC), and intracellular-weighted sodium signal (inversion recovery (IR) and triple quantum filter (TQF) sequence). In addition, the FSHD patients underwent muscle strength testing.ResultsImaging biomarkers related with water mobility (wT1 and wT2) and ion homeostasis (TSC, IR, TQF) were increased in muscles of FSHD patients. Muscle groups with FF > 10% had higher wT2, wT1, TSC, IR, and TQF values than muscles with FF < 10%. Muscles with FF < 10% resembled muscles of healthy controls for these MRI disease activity measures. However, wT1 was increased in few muscles without fat replacement. Furthermore, few STIR-negative muscles (n = 11/76) exhibited increased wT1, TSC, IR or TQF. Increased wT1 as well as 23Na signals were also present in muscles with normal wT2. Muscle strength was related to the mean FF and all imaging biomarkers of tibialis anterior except wT2 were correlated with dorsal flexion.ConclusionThe newly evaluated imaging biomarkers related with water mobility (wT1) and ion homeostasis (TSC, IR, TQF) showed different patterns compared to the established markers like FF in muscles of FSHD patients. These quantitative biomarkers could thus contain valuable complementary information for the early characterization of disease progression.

Intracellular Sodium Changes in Cancer Cells Using a Microcavity Array-Based Bioreactor System and Sodium Triple-Quantum MR Signal

The sodium triple-quantum (TQ) magnetic resonance (MR) signal created by interactions of sodium ions with macromolecules has been demonstrated to be a valuable biomarker for cell viability. The aim of this study was to monitor a cellular response using the sodium TQ signal during inhibition of Na/K-ATPase in living cancer cells (HepG2). The cells were dynamically investigated after exposure to 1 mM ouabain or K+-free medium for 60 min using an MR-compatible bioreactor system. An improved TQ time proportional phase incrementation (TQTPPI) pulse sequence with almost four times TQ signal-to-noise ratio (SNR) gain allowed for conducting experiments with 12–14 × 106 cells using a 9.4 T MR scanner. During cell intervention experiments, the sodium TQ signal increased to 138.9 ± 4.1% and 183.4 ± 8.9% for 1 mM ouabain (n = 3) and K+-free medium (n = 3), respectively. During reperfusion with normal medium, the sodium TQ signal further increased to 169.2 ± 5.3% for the ouabain experiment, while it recovered to 128.5 ± 6.8% for the K+-free experiment. These sodium TQ signal increases agree with an influx of sodium ions during Na/K-ATPase inhibition and hence a reduced cell viability. The improved TQ signal detection combined with this MR-compatible bioreactor system provides a capability to investigate the cellular response of a variety of cells using the sodium TQ MR signal.

Control of surface plasmon-polaritons at interfaces between triple quantum dots and nanocomposites

Surface plasmon-polariton (SPPs) at the interface between a nanocomposite material and a medium, in which triple quantum dots (QDs) are uniformely embedded, are theoretically investigated. The absorption and dispersion spectra of SPPs are shown to have interesting behavior in the proposed system. The plasmonic spectra can be efficiently controlled via gate voltages applied in the triple QD as well as the filling ratio of nanoparticles in the composite. Moreover, the effect of incident frequencies on different features of the propagating plasmons is also manipulated. The propagation length and plasmonic depth are measured with different spectroscopic parameters. This study provides more degrees of freedom for generation and control of SPPs in plasmonic geometries containing QDs or nanocomposites or both. The results may find significant applications in atomic spectroscopy, nano-photonics, photovoltaic devices, biosensors and plasmonster technology.

Theory of magnetotransport in shaped topological insulator nanowires

We show that shaped topological insulator (TI) nanowires, i.e. such that their cross-section radius varies along the wire length, can be tuned into a number of different transport regimes when immersed in a homogeneous coaxial magnetic field. This is in contrast with widely studied tubular nanowires with constant cross-section, and is due to magnetic confinement of Dirac surface carriers. In flat 2D systems such a confinement requires non-homogeneous magnetic fields, while for shaped nanowires of standard size homogeneous fields of the order of $B\sim\,1$T are sufficient. We put recent work [Kozlovsky et al., Phys. Rev. Lett. 124, 126804 (2020)] into broader context and extend it to deal with axially symmetric wire geometries with arbitrary radial profile. A dumbbell-shaped TI nanowire is used as a paradigmatic example for transport through a constriction and shown to be tunable into five different transport regimes: (i) conductance steps, (ii) resonant transmission, (iii) current suppression, (iv) Coulomb blockade, and (v) transport through a triple quantum dot. Switching between regimes is achieved by modulating the strength of a coaxial magnetic field and does not require strict axial symmetry of the wire cross-section. As such, it should be observable in TI nanowires fabricated with available experimental techniques.

Electronic characteristics of asymmetric triple GaAlAs/GaAs and GaInAs/GaAs quantum wells depending on Al and In concentration

Herein, the electronic characteristics of asymmetric triple Ga1-x Alx As/GaAs quantum wells (A model) and Ga1-x Inx As/GaAs quantum wells (B model) have been examined as dependent on Al and In concentration. The energy levels, the wave functions and the finding probability of electron in quantum well (QW) of these systems under effective mass approach were concluded by Schrödinger equation solution. According to our results, the main differences between models A and B are effective mass and energy gap. For A model, GaAlAs is the barrier and GaAs is the well. Whereas for B model, GaAs is the barrier and GaInAs is the well. Also, the energy levels and the potential height of B model are unceasingly higher than of B model. The concentration ratio has a great impact on the electronic features of the asymmetric triple quantum well (ATQW). These features have a convenient attention for the purpose of adjustable semiconductor devices.

Parity-time symmetry and asymmetric diffraction of light in four-level triple quantum wells

In this paper, we investigate two-dimensional parity-time (PT) symmetry and electromagnetically induced grating (EIG) in four-level asymmetric triple quantum wells (QWs). Here, PT-symmetry and EIG are realized by appropriately varying the detuning value of the probe, and the modulation amplitudes of a coupling field and standing wave (SW) pump. By virtue of its PT symmetry, the EIG asymmetrically diffracts the probe beam. The angular switching of the diffracted beam can be achieved either by varying the probe or the coupling and SW pump fields. The intensity distribution of the diffracted beam over higher-order diffraction peaks depends on the interaction length in the QW. For small interaction lengths, most of the energy is distributed close to the central diffraction peak. With an increase in the interaction length, energy is gradually transferred to higher order diffraction peaks.

Structure of type A CAI-like melts: A view from multi-nuclear NMR study of melilite (Ca2Al2SiO7-Ca2MgSi2O7) glasses

Exploring the polymerization and structural disorder of Ca-Al-rich inclusion (CAI)-like melts is a key question in cosmochemistry due to strong implications for macroscopic properties of melts (i.e., viscosity and diffusivity). Here, we report experimental results showing the effect of composition on the structure of melilite glasses and melts [åkermanite (Åk, Ca2MgSi2O7) - gehlenite (Gh, Ca2Al2SiO7)] in type A CAIs with varying composition using high-resolution solid-state nuclear magnetic resonance (NMR). The 27Al magic angle spinning (MAS) and 3Q (triple quantum) MAS NMR spectra of melilite glasses show predominant [4]Al. A non-negligible fraction of [5]Al is observed in Åk50Gh50 and Åk72Gh28 glasses and it slightly increases with increasing åkermanite content. The 17O 3QMAS NMR spectra of melilite glasses show that bridging oxygens (BOs, Si–O–Si, Al–O–Al, and Si–O–Al) and non-bridging oxygens (NBOs, Ca–O-Si, Ca-O-Al, and mixed {Ca, Mg}–NBO) are partially resolved. Despite the strong preference of Si over Al for NBOs, for the first time, Ca-O-Al is observed in natural melts (i.e., gehlenite and Åk25Gh75 glasses and melts). The results show that Al-NBO (~150 ppm in MAS dimension) can be distinguished from Si-NBO (~110 ppm) in melilite glasses and melts. The fraction of NBO increases with increasing åkermanite content. The experimental results suggest that composition-induced structural changes should be considered to interpret the melt viscosity, diffusivity, and oxygen isotopic composition of CAI-like melts in the early Solar System.

Controllable double tunneling induced optical soliton storage in linear triple quantum dot molecules

We propose an asymmetric linear triple quantum dot molecule model for a recent experimental device with a double neighboring dot-dot tunneling coupling, of which the linear and nonlinear dynamical properties are analytically studied by using an amplitude variable approach combined with multi-scale method. It is shown that double transparency windows are formed by the double tunneling coupling. Both dark and bright optical solitons are then obtained, of which both the types and the propagating velocity can be controlled by the two tunneling coupling strengths. Interestingly, the propagating velocity of the solitons can approach to zero at certain tunneling coupling strengths, the motionless optical solitons appearing there. The results indicate potential applications of the semiconductor quantum devices for optical soliton storage.

Physically defined silicon triple quantum dots charged with few electrons in metal-oxide-semiconductor structures

Physically defined silicon triple quantum dots (TQDs) are fabricated on a silicon-on-insulator substrate by dry-etching. The fabrication method enables us to realize a simple structure that does not require gates to create quantum dot confinement potentials and is highly advantageous for integration. We observe the few-electron regime and resonant tunneling points in the TQDs by applying voltages to two plunger gates at a temperature of 4.2 K. Moreover, we reproduce the measured charge stability diagram by simulation with an equivalent-circuit model composed of capacitors and resistors. The equivalent-circuit simulation makes it clear that we realize three QDs in series within the nanowire, as planned. This circuit model also elucidates the mechanism of resonant tunneling and identifies a quadruple point of TQDs.

Relocalization switch in a triple quantum dot molecule in 2D

A symmetric chain of three quantum dots (i.e., one of the simplest quantum dot molecules) is constructed using a three-parametric non-separable version of an asymptotically separable sextic polynomial potential [Formula: see text]. The probability density [Formula: see text] (admitting either the central or off-central dominance) is assumed measured. A dynamical regime is found with an enhanced sensitivity of the central—off-central transition to the parameters. Quantitatively, the possibility of control of such a switch alias “relocalization catastrophe” is illustrated non-numerically.

Simplifying LR-HSQC spectra using a triple-quantum filter: The LR-HTQC experiment.

Long-range heteronuclear single quantum correlation (LR-HSQC) experiments may be applied for detecting long-range correlations but suffer from two disadvantages, common to all heteronuclear long-range correlation experiments: (i) The information density in LR-HSQC spectra may be too high to be used directly without "filtering out" shorter range correlations, and (ii) often, substantial differences in intensity among cross peaks exist, potentially hampering the visualization of weak, often crucial cross peaks. In this contribution, we propose a modified LR-HSQC experiment, the LR-HTQC experiment (Long-Range Heteronuclear Triple Quantum Correlation) that partially solves the problems aforementioned. We show theoretically and experimentally that the LR-HTQC experiment removes the intense cross peaks of CH spin pairs, substantially reduces the medium intensity of cross peaks originating from CHH' spin systems, whereas the typically weak intensity of cross peaks of CHH'H″ and C(H)n, n > 3 spin systems is less affected. Consequently, the LR-HTQC experiment affords simplified long-range heteronuclear shift correlation spectra and scales down large intensity differences among different types of cross peaks, although a certain general reduction of signal intensities has to be accepted.