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Guang-Yao Huang

Publications and source records attributed to Guang-Yao Huang.

At least 19 recordsLinked to original sources

Experimental review on Majorana zero-modes in hybrid nanowires

As the condensed matter analog of Majorana fermion, the Majorana zero-mode is well known as a building block of fault-tolerant topological quantum computing. This review focuses on the recent progress of Majorana experiments, especially experiments about semiconductor-superconductor hybrid devices. We first sketch Majorana zero-mode formation from a bottom-up view, which is more suitable for beginners and experimentalists. Then, we survey the status of zero-energy state signatures reported recently, from zero-energy conductance peaks, the oscillations, the quantization, and the interactions with extra degrees of freedom. We also give prospects of future experiments for advancing one-dimensional semiconductor nanowire-superconductor hybrid materials and devices.

cond-mat.mes-hall↗

Nonequilibrium dynamics of the localization-delocalization transition in the non-Hermitian Aubry-André model

In this paper, we investigate the driven dynamics of the localization transition in the non-Hermitian Aubry-André model with the periodic boundary condition. Depending on the strength of the quasi-periodic potential $λ$, this model undergoes a localization-delocalization phase transition. We find that the localization length $ξ$ satisfies $ξ\sim \varepsilon^{-ν}$ with $\varepsilon$ being the distance from the critical point and $ν=1$ being a universal critical exponent independent of the non-Hermitian parameter. In addition, from the finite-size scaling of the energy gap between the ground state and the first excited state, we determine the dynamic exponent $z$ as $z=2$. The critical exponent of the inverse participation ratio (IPR) for the $n$th eigenstate is also determined as $s=0.1197$. By changing $\varepsilon$ linearly to cross the critical point, we find that the driven dynamics can be described by the Kibble-Zurek scaling (KZS). Moreover, we show that the KZS with the same set of the exponents can be generalized to the localization phase transitions in the excited states.

cond-mat.dis-nn↗

Cascade of the delocalization transition in a non-Hermitian interpolating Aubry-Andr{é}-Fibonacci chain

In this paper, the interplay of the non-Herimiticity and the cascade of delocalization transition in the quasi-periodic chain is studied. The study is applied in a non-Hermitian interpolating Aubry-Andr{é}-Fibonacci (IAAF) model, which combines the non-Hermitian Aubry-Andr{é} (AA) model and the non-Hermitian Fibonacci model through a varying parameter, and the non-Hermiticity in this model is introduced by the non-reciprocal hopping. In the non-Hermitian AA limit, the system undergoes a delocalization transition by tuning the potential strength. At the critical point, the spatial distribution of the critical state shows a self-similar structure with the relative distance between the peaks being the Fibonacci sequence, and the finite-size scaling of the inverse participation ratios $({\rm IPRs})$ of the critical ground state with lattice size $L$ shows that ${\rm IPR}_g\propto L^{-0.1189}$. In the non-Hermitian Fibonacci limit, we find that the system is always in the extended phase. Along the continuous deformation from the non-Hermitian AA model into the non-Hermitian Fibonacci model in the IAAF model, the cascade of the delocalization transition is found, but only a few plateaux appear. Moreover, the self-similar structure of spatial distribution for the critical modes along the cascade transition is also found. In addition, we find that the delocalization transition and the real-complex transition for the excited states happen at almost the same parameter. Our results show that the non-Hermiticity provides an additional knob to control the cascade of the delocalization transition besides the on-site potential.

cond-mat.dis-nn↗

Highly tunable quadruple quantum dot in a narrow bandgap semiconductor InAs nanowire

Quantum dots (QDs) made from semiconductors are among the most promising platforms for the developments of quantum computing and simulation chips, and have advantages over other platforms in high density integration and in compatibility to the standard semiconductor chip fabrication technology. However, development of a highly tunable semiconductor multiple QD system still remains as a major challenge. Here, we demonstrate realization of a highly tunable linear quadruple QD (QQD) in a narrow bandgap semiconductor InAs nanowire with fine finger gate technique. The QQD is studied by electron transport measurements in the linear response regime. Characteristic two-dimensional charge stability diagrams containing four groups of resonant current lines of different slopes are found for the QQD. It is shown that these current lines can be individually assigned as arising from resonant electron transport through the energy levels of different QDs. Benefited from the excellent gate tunability, we also demonstrate tuning of the QQD to regimes where the energy levels of two QDs, three QDs and all the four QDs are energetically on resonance, respectively, with the fermi level of source and drain contacts. A capacitance network model is developed for the linear QQD and the simulated charge stability diagrams based on the model show good agreements with the experiments. Our work presents a solid experimental evidence that narrow bandgap semiconductor nanowires multiple QDs could be used as a versatile platform to achieve integrated qubits for quantum computing and to perform quantum simulations for complex many-body systems.

cond-mat.mes-hall↗

Quantum Hall admittance in non-Hermitian systems

We propose a pair of the complex Berry curvatures associated with the non-Hermitian Hamiltonian and its Hermitian adjoint to reveal new physics in non-Hermitian systems. We give the complex Berry curvature and Berry phase for the two-dimensional non-Hermitian Dirac model. The imaginary part of the complex Berry phase induces the quantum Hall susceptance such that the quantum Hall conductance is generalized to quantum Hall admittance for non-Hermitian systems, which implies that the non-Hermiticity of systems could induce an intrinsic quantum capacitance or inductance of systems depending on the non-Hermitian parameters. We analyze the complex energy band structures of the two-dimensional non-Hermitian Dirac model and demonstrate the point and line gaps and their closings as the exceptional degeneracy of the energy bands in the parameter space, which are associated with topological phases. In the continuum limit, we obtain the complex Berry phase in the parameter space.

quant-ph↗

Measurements of anisotropic g-factors for electrons in InSb nanowire quantum dots

We have measured the Zeeman splitting of quantum levels in few-electron quantum dots (QDs) formed in narrow bandgap InSb nanowires via the Schottky barriers at the contacts under application of different spatially orientated magnetic fields. The effective g-factor tensor extracted from the measurements is strongly anisotropic and level-dependent, which can be attributed to the presence of strong spin-orbit interaction (SOI) and asymmetric quantum confinement potentials in the QDs. We have demonstrated a successful determination of the principal values and the principal axis orientations of the g-factor tensors in an InSb nanowire QD by the measurements under rotations of a magnetic field in the three orthogonal planes. We also examine the magnetic-field evolution of the excitation spectra in an InSb nanowire QD and extract a SOI strength of $Δ_{so}\sim 180$ $μ$eV from an avoided level crossing between a ground state and its neighboring first excited state in the QD.

cond-mat.mes-hall↗

Many-body localization in a non-Hermitian quasi-periodic system

In the present study, the interplay among interaction, topology, quasiperiodicity, and non-Hermiticity is studied. The hard-core bosons model on a one-dimensional lattice with asymmetry hoppings and quasiperiodic onsite potentials is selected. This model, which preserves time-reversal symmetry (TRS), will exhibit three types of phase transition: real-complex transition of eigenenergies, topological phase transition and many-body localization (MBL) phase transition. For thereal-complex transition, it is found that the imaginary parts of the eigenenergies are always suppressed by the MBL. Moreover, by calculating the winding number, a topological phase transition can be revealed with the increase of potential amplitude, and we find that the behavior is quite different from the single-particle systems. Based on our numerical results, we conjecture that these three types of phase transition occur at the same point in the thermodynamic limit, and the MBL transition of quasiperiodic system and disordered system should belong to different universality classes. Finally, we demonstrate that these phase transitions can profoundly affect the dynamics of the non-Hermitian many-body system.

cond-mat.dis-nn↗

Enhancement of optomechanically induced sum sideband using parametric interactions

We theoretically study radiation pressure induced generation of the frequency components at the sum sideband in an optomechanical system containing an optical parametric amplifier (OPA). It is shown that an OPA inside a cavity can considerably enhance the amplitude of sum sideband even with low power input fields. We find a new matching condition for the upper sum sideband generation. The height and width of the new peak can be adjusted by the nonlinear gain of the OPA. Furthermore, the lower sum sideband generation can be enhanced with several orders of magnitude by tuning the nonlinear gain parameter and the phase of the field pumping the OPA. The enhanced sum sideband may have potential applications to the manipulation of light in a on-chip optomechanical device and the sensitively sensing for precision measurement in the weak optomechanical coupling regime.

physics.optics↗

Anisotropic Pauli spin-blockade effect and spin-orbit interaction field in an InAs nanowire double quantum dot

We report on experimental detection of the spin-orbit interaction field in an InAs nanowire double quantum dot device. In the spin blockade regime, leakage current through the double quantum dot is measured and is used to extract the effects of spin-orbit interaction and hyperfine interaction on spin state mixing. At finite magnetic fields, the leakage current arising from the hyperfine interaction is suppressed and the spin-orbit interaction dominates spin state mixing. We observe dependence of the leakage current on the applied magnetic field direction and determine the direction of the spin-orbit interaction field. We show that the spin-orbit field lies in a direction perpendicular to the nanowire axis but with a pronounced off-substrate-plane angle. It is for the first time that such an off-substrate-plane spin-orbit field in an InAs nanowire has been detected. The results are expected to have an important implication in employing InAs nanowires to construct spin-orbit qubits and topological quantum devices.

cond-mat.mes-hall↗

Charge transport and electron-hole asymmetry in low-mobility graphene/hexagonal boron nitride heterostructures

Graphene/hexagonal boron nitride (G/$h$-BN) heterostructures offer an excellent platform for developing nanoelectronic devices and for exploring correlated states in graphene under modulation by a periodic superlattice potential. Here, we report on transport measurements of nearly $0^{\circ}$-twisted G/$h$-BN heterostructures. The heterostructures investigated are prepared by dry transfer and thermally annealing processes and are in the low mobility regime (approximately $3000~\mathrm{cm}^{2}\mathrm{V}^{-1}\mathrm{s}^{-1}$ at 1.9 K). The replica Dirac spectra and Hofstadter butterfly spectra are observed on the hole transport side, but not on the electron transport side, of the heterostructures. We associate the observed electron-hole asymmetry to the presences of a large difference between the opened gaps in the conduction and valence bands and a strong enhancement in the interband contribution to the conductivity on the electron transport side in the low-mobility G/$h$-BN heterostructures. We also show that the gaps opened at the central Dirac point and the hole-branch secondary Dirac point are large, suggesting the presence of strong graphene-substrate interaction and electron-electron interaction in our G/$h$-BN heterostructures. Our results provide additional helpful insight into the transport mechanism in G/$h$-BN heterostructures.

cond-mat.mes-hall↗

Majorana bound states and subgap states in three-terminal topological superconducting nanowire-quantum dot hybrid devices

Three-terminal topological superconducting nanowire (TSNW)-quantum dot (QD) hybrid junction devices are studied. The energy spectra and the wave functions of the subgap states are calculated as a function of the superconducting phase differences between TSNWs and as a function of the QD level energy based on the Bogoliubov-de Gennes tight-binding Hamiltonians. It is shown that when the QD level is located near or inside the superconducting gap, there can exist eight subgap states. Among them, four low energy (two positive and two negative) subgap states are essentially formed by linear combinations of the six Majorana bound states (MBSs) located at the ends of the three TSNWs. The remaining four high energy subgap states are mainly built from linear combinations of the QD state and the three MBSs of the TSNWs adjacent to the QD. When there is no QD level near or inside the superconducting gap, only six subgap states built from linear combinations of the six MBSs of the three TSNWs can be present in the system. It is also shown that there exists a unique point in the parameter space of the superconducting phase differences between TSNWs, at which the energies of the six low energy subgap states move close to each other towards nearly zero energies. Simple but general effective model Hamiltonians for the three-terminal TSNW-QD hybrid devices have also been developed. Based on the effective model Hamiltonians, the subgap states of the three-terminal TSNW-QD hybrid devices in the limit of the three infinitely long TSNWs are studied. The results of the calculations and the effective model Hamiltonians could be used as a starting point to construct and investigate the braiding schemes of MBSs in TSNW junction devices.

cond-mat.mes-hall↗

Coherent transport in a linear triple quantum dot made from a pure-phase InAs nanowire

A highly tunable linear triple quantum dot (TQD) device is realized in a single-crystalline pure-phase InAs nanowire using a local finger gate technique. The electrical measurements show that the charge stability diagram of the TQD can be represented by three kinds of current lines of different slopes and a simulation performed based on a capacitance matrix model confirms the experiment. We show that each current line observable in the charge stability diagram is associated with a case where a QD is on resonance with the Fermi level of the source and drain reservoirs. At a triple point where two current lines of different slopes move together but show anti-crossing, two QDs are on resonance with the Fermi level of the reservoirs. We demonstrate that an energetically degenerated quadruple point, at which all three QDs are on resonance with the Fermi level of the reservoirs, can be built by moving two separated triple points together via sophistically tuning of energy levels in the three QDs. We also demonstrate the achievement of direct coherent electron transfer between the two remote QDs in the TQD, realizing a long-distance coherent quantum bus operation. Such a long-distance coherent coupling could be used to investigate coherent spin teleportation and super-exchange effects and to construct a spin qubit with an improved long coherent time and with spin state detection solely by sensing the charge states.

cond-mat.mes-hall↗

Majorana fermions in topological insulator nanowires: from single superconducting nanowires to Josephson junctions

Signatures of Majorana fermion bound states in one-dimensional topological insulator (TI) nanowires with proximity effect induced superconductivity are studied. The phase diagram and energy spectra are calculated for single TI nanowires and it is shown that the nanowires can be in the topological invariant phases of winding numbers $W=0, \pm 1$, and $\pm 2$ corresponding to the cases with zero, one and two pairs of Majorana fermions in the single TI nanowires. It is also shown that the topological winding numbers, i.e., the numbers of pairs of Majorana fermions in the TI nanowires can be extracted from the transport measurements of a Josephson junction device made from two TI nanowires, while the sign in the winding numbers can be extracted using a superconducting quantum interference device (SQUID) setup.

cond-mat.mes-hall↗

Kibble-Zurek scaling in the Yang-Lee edge singularity

We study the driven dynamics across the critical points of the Yang-Lee edge singularities (YLESes) in a finite-size quantum Ising chain with an imaginary symmetry-breaking field. In contrast to the conventional classical or quantum phase transitions, these phase transitions are induced by tuning the strength of the dissipation in a non-Hermitian system and can occur even at finite size. For conventional phase transitions, universal behaviors in driven dynamics across critical points are usually described by the Kibble-Zurek mechanism, which states that the scaling in dynamics is dictated by the critical exponents associated with one critical point and topological defects will emerge after the quench. While the mechanism leading to topological defects breaks down in the YLES, we find that for small lattice size, the driven dynamics can still be described by the Kibble-Zurek scaling with the exponents determined by the $(0+1)$-dimensional YLES. For medium finite size, however, the driven dynamics can be described by the Kibble-Zurek scaling with two sets of critical exponents determined by both the $(0+1)$-dimensional and the $(1+1)$-dimensional YLESes.

cond-mat.stat-mech↗

Orbital magnetic phase and pure persistent spin current in spin-orbit coupling mesoscopic rings

By solving the Rashba model of mesoscopic rings, we give analytically the ground-state properties of the ring, including the spin polarization, the persistent charge and spin currents (PCC and PSC). These ground-state properties can be given based on four kinds of electron numbers in rings. The effect of the self-inductance of the ring leads to the self-sustained magnetic flux (SSMF) and the self-sustained PCC and PSC, which break spontaneously time-reversal symmetry to form orbital magnetic phase (OMP). To tune the spin-orbit coupling strength or electron number of the ring can induce the phase transition between the OMP and non-OMP. For exact one-dimensional rings we find the coexistence of the pure PSC and SSMF. This property of the pure PSC may provide a new scheme to measure the pure PSC.

cond-mat.mes-hall↗

Theory of spin polarization in mesoscopic spin-orbit coupling systems

We establish a general formalism of the bulk spin polarization (BSP) and the current-based spin polarization (CSP) for mesoscopic ferromagnetic and spin-orbit interaction (SOI) semiconducting systems. Based on this formalism, we reveal the basic properties of BSP and CSP and their relationships. The BSP describes the intrinsic spin polarized properties of devices. The CSP depends on both intrinsic parameters of device and the incident current. For the non-spin-polarized incident current with the inphase spin-phase coherence, CSP equals to BSP. We give analytically the BSP and CSP of several typical nanodevice models, ferromagnetic nanowire, Rashba nanowire and rings. These results provide basic physical behaviors of BSP and CSP and their relationships.

cond-mat.mes-hall↗

Topological invariance and global Berry phase in non-Hermitian systems

By studying the topological invariance andBerry phase in non-Hermitian systems, we reveal the basic properties of the complex Berry phase and generalize the global Berry phases Q to identify the topological invariance for non-Hermitian systems.We find thatQcan identify topological invariance in two kinds of non-Hermitian model, the two-level non-Hermitian Hamiltonian and the bipartite dissipative model. For the bipartite dissipative model, an abrupt change of the Berry phase in the parameter space reveals a quantum phase transition and is related to the exceptional points. These results give the basic relationships between the Berry phase and the quantum and topological phase transitions of non-Hermitian systems.

quant-ph↗

Detecting Noncommutative Phase Space by Aharonov-Bohm Effect

Noncommutative phase space plays an essential role in particle physics and quantum gravity at the Planck scale. However, direct experimental evidence or observation to demonstrate the existence of noncommutative phase space is still lacking.We study a quantum ring in noncommutative phase space based on the Seiberg-Witten map and give the effective magnetic potential and field coming from the noncommutative phase space, which induces the persistent current in the ring. We introduce two variables as two signatures to detect the noncommutative phase space and propose an experimental scheme to detect the noncommutative phase space as long as we measure the persistent current and the external magnetic flux.

quant-ph↗