arXiv subjects

Dong Pan

Publications and source records attributed to Dong Pan.

At least 55 records · Page 3Linked to original sources

arXiv2022

Electrically tunable spin-orbit interaction in an InAs nanosheet

We report on an experimental study of the spin-orbit interaction (SOI) in an epitaxially grown free-standing InAs nanosheet in a dual-gate field-effect device. Gate-transfer characteristic measurements show that independent tunings of the carrier density in the nanosheet and the potential difference across the nanosheet can be efficiently achieved with use of the dual gate. The quantum transport characteristics of the InAs nanosheet are investigated by magnetoconductance measurements at low temperatures. It is shown that the electron transport in the nanosheet can be tuned from the weak antilocalization to the weak localization and then back to the weak antilocalization regime with a voltage applied over the dual gate without a change in carrier density. The spin-orbit length extracted from the magnetoconductance measurements at a constant carrier density exhibits a peak value at which the SOI of the Rashba type is suppressed and the spin relaxation due to the presence of an SOI of the Dresselhaus type in the nanosheet can be revealed. Energy band diagram simulations have also been carried out for the device at the experimental conditions and the physical insights into the experimental observations have been discussed in light of the results of simulations.

cond-mat.mes-hall↗

arXiv2022

Fabrication and characterization of InSb nanosheet/hBN/graphite heterostructure devices

Semiconductor InSb nanosheet/hexagonal boron nitride (hBN)/graphite trilayers are fabricated, and single- and double-gate devices made from the trilayers are realized and characterized. The InSb nanosheets employed in the trilayer devices are epitaxially grown, free-standing, zincblende crystals and are in micrometer lateral sizes. The hBN and graphite flakes are obtained by exfoliation. Each trilayer is made by successively stacking an InSb nanosheet on an hBN flake and on a graphite flake using a home-made alignment stacking/transfer setup. The fabricated single- and double-gate devices are characterized by electrical and/or magnetotransport measurements. In all these devices, the graphite and hBN flakes are employed as the bottom gates and the gate dielectrics. The measurements of a fabricated single bottom-gate field-effect device show that the InSb nanosheet in the device has an electron field-effect mobility of ~7300 cm$^2$V$^{-1}$s$^{-1}$ and a low gate hysteresis of ~0.05 V at 1.9 K. The measurements of a double-gate Hall-bar device show that both the top and the bottom gate exhibit strong capacitive couplings to the InSb nanosheet channel and can thus tune the nanosheet channel conduction effectively. The electron Hall mobility in the InSb nanosheet of the Hall-bar device is extracted to be larger than 1.1$\times$10$^4$ cm$^2$V$^{-1}$s$^{-1}$ at a sheet electron density of ~6.1$\times$10$^{11}$ cm$^{-2}$ and 1.9 K and, thus, the device exhibits well-defined Shubnikov-de Haas oscillations.

cond-mat.mes-hall↗

arXiv2022

Quantum oscillations in a hexagonal boron nitride-supported single crystalline InSb nanosheet

A gated Hall-bar device is made from an epitaxially grown, free-standing InSb nanosheet on a hexagonal boron nitride (hBN) dielectric/graphite gate structure and the electron transport properties in the InSb nanosheet are studied by gate-transfer characteristic and magnetotransport measurements at low temperatures. The measurements show that the carriers in the InSb nanosheet are of electrons and the carrier density in the nanosheet can be highly efficiently tuned by the graphite gate. The mobility of the electrons in the InSb nanosheet is extracted from low-field magneotransport measurements and a value of the mobility exceeding ~18000 cm$^2$V$^{-1}$s$^{-1}$ is found. High-field magentotransport measurements show well-defined Shubnikov-de Haas (SdH) oscillations in the longitudinal resistance of the InSb nanosheet. Temperature-dependent measurements of the SdH oscillations are carried out and key transport parameters, including the electron effective mass m$^*$$\sim$0.028 m$_0$ and the quantum lifetime $τ$$\sim$0.046 ps, in the InSb nanosheet are extracted. It is for the first time that such experimental measurements have been reported for a free-standing InSb nanosheet and the results obtained indicate that InSb nanosheet/hBN/graphite gate structures can be used to develop advanced quantum devices for novel physics studies and for quantum technology applications.

cond-mat.mes-hall↗

arXiv2022

Large Andreev bound state zero bias peaks in a weakly dissipative environment

We study Andreev bound states in hybrid InAs-Al nanowire devices. The energy of these states can be tuned to zero by gate voltage or magnetic field, revealing large zero bias peaks (ZBPs) near 2e^2/h in tunneling conductance. Probing these large ZBPs using a weakly dissipative lead reveals non-Fermi liquid temperature (T) dependence due to environmental Coulomb blockade (ECB), an interaction effect from the lead acting on the nanowire junction. By increasing T, these large ZBPs either show a height increase or a transition from split peaks to a ZBP, both deviate significantly from non-dissipative devices where a Fermi-liquid T dependence is revealed. Our result demonstrates the competing effect between ECB and thermal broadening on Andreev bound states.

cond-mat.mes-hall↗

arXiv2022

An Evolutionary Pathway for the Quantum Internet Relying on Secure Classical Repeaters

Until quantum repeaters become mature, quantum networks remain restricted either to limited areas of directly connected nodes or to nodes connected to a common node. We circumvent this limitation by conceiving quantum networks using secure classical repeaters combined with the quantum secure direct communication (QSDC) principle, which is a compelling form of quantum communication that directly transmits information over quantum channel. The final component of this promising solution is our classical quantum-resistant algorithm. Explicitly, in these networks, the ciphertext gleaned from a quantum-resistant algorithm is transmitted using QSDC along the nodes, where it is read out and then transmitted to the next node. At the repeaters, the information is protected by our quantum-resistant algorithm, which is secure even in the face of a quantum computer. Hence, our solution offers secure end-to-end communication across the entire network, since it is capable of both eavesdropping detection and prevention in the emerging quantum internet. It is compatible with operational networks, and will enjoy the compelling services of the popular Internet, including authentication. Hence, it smoothens the transition from the classical Internet to the Quantum Internet (Qinternet) by following a gradual evolutionary upgrade. It will act as an alternative network in quantum computing networks in the future. We have presented the first experimental demonstration of a secure classical repeater based hybrid quantum network constructed by a serial concatenation of an optical fiber and free-space communication link. In conclusion, secure repeater networks may indeed be constructed using existing technology and continue to support a seamless evolutionary pathway to the future Qinternet of quantum computers.

quant-ph↗

arXiv2021

Large-composition-range pure-phase homogeneous InAs$_{1-x}$Sb$_x$ nanowires

Narrow bandgap InAs$_{1-x}$Sb$_x$ nanowires show broad prospects for applications in wide spectrum infrared detectors, high-performance transistors and quantum computation. Realizing such applications require the fine control of composition and crystal structure of nanowires. However, to date, the fabrication of large-composition-range pure-phase homogeneous InAs$_{1-x}$Sb$_x$ nanowires remains a huge challenge. Here, we first report the growth of large-composition-range stemless InAs$_{1-x}$Sb$_x$ nanowires (x = 0-0.63) on Si (111) substrates by molecular-beam epitaxy. It is found that pure-phase InAs$_{1-x}$Sb$_x$ nanowires can be successfully obtained by controlling the antimony content x, nanowire diameter and nanowire growth direction. Detailed EDS data show that the antimony is uniformly distributed along the axial and radial directions of InAs$_{1-x}$Sb$_x$ nanowires and no spontaneous core-shell nanostructures form in the nanowires. Based on field-effect measurements, we confirm that InAs$_{1-x}$Sb$_x$ nanowires exhibit good conductivity and their mobilities can be up to 4200 cm^2/V.s at 7 K. Our work lays the foundation for the development of InAs$_{1-x}$Sb$_x$ nanowire optoelectronic, electronic and quantum devices.

physics.app-ph↗

arXiv2021

Suppressing Andreev bound state zero bias peaks using a strongly dissipative lead

Hybrid semiconductor-superconductor nanowires are predicted to host Majorana zero modes, manifested as zero-bias peaks (ZBPs) in tunneling conductance. ZBPs alone, however, are not sufficient evidence due to the ubiquitous presence of Andreev bound states in the same system. Here, we implement a strongly resistive normal lead in our InAs-Al nanowire devices and show that most of the expected ZBPs, corresponding to zero-energy Andreev bound states, can be suppressed, a phenomenon known as environmental Coulomb blockade. Our result is the first experimental demonstration of this dissipative interaction effect on Andreev bound states and can serve as a possible filter to narrow down ZBP phase diagram in future Majorana searches.

cond-mat.mes-hall↗

arXiv2021

Generic Security Analysis Framework for Quantum Secure Direct Communication

Quantum secure direct communication provides a direct means of conveying secret information via quantum states among legitimate users. The past two decades have witnessed its great strides both theoretically and experimentally. However, the security analysis of it still stays in its infant. Some practical problems in this field to be solved urgently, such as detector efficiency mismatch, side-channel effect and source imperfection, are propelling the birth of a more impeccable solution. In this paper, we establish a new framework of the security analysis driven by numerics where all the practical problems may be taken into account naturally. We apply this framework to several variations of the DL04 protocol considering real-world experimental conditions. Also, we propose two optimizing methods to process the numerical part of the framework so as to meet different requirements in practice. With these properties considered, we predict the robust framework would open up a broad avenue of the development in the field.

quant-ph↗

arXiv2021

Large zero bias peaks and dips in a four-terminal thin InAs-Al nanowire device

We report electron transport studies of a thin InAs-Al hybrid semiconductor-superconductor nanowire device using a four-terminal design. Compared to previous works, thinner InAs nanowire (diameter less than 40 nm) is expected to reach fewer sub-band regime. The four-terminal device design excludes electrode contact resistance, an unknown value which has inevitably affected previously reported device conductance. Using tunneling spectroscopy, we find large zero-bias peaks (ZBPs) in differential conductance on the order of $2e^2/h$. Investigating the ZBP evolution by sweeping various gate voltages and magnetic field, we find a transition between a zero-bias peak and a zero-bias dip while the zero-bias conductance sticks close to $2e^2/h$. We discuss a topologically trivial interpretation involving disorder, smooth potential variation and quasi-Majorana zero modes.

cond-mat.mes-hall↗

arXiv2021

Charge detection of a quantum dot under different tunneling barrier symmetries and bias voltages

We report on the realization of a coupled quantum dot (QD) system containing two single QDs made in two adjacent InAs nanowires. One QD (sensor QD) is used as a charge sensor to detect the charge state transition in the other QD (target QD). We investigate the effect of the tunneling barrier asymmetry of the target QD on the detection visibility of charge state transition in the target QD. The charge stability diagrams of the target QD under different configurations of barrier-gate voltages are simultaneously measured via the direct signals of electron transport through the target QD and via the detection signals of charge state transition in the target QD from the sensor QD. We find that the complete Coulomb diamond boundaries of the target QD and the transport processes involving the excited states in the target QD can be observed in the transconductance signals of the sensor QD only when the tunneling barriers of the target QD are nearly symmetric. These phenomena are explained by analyzing the effect of the ratio of the two tunneling rates on the electron transport processes through the target QD. Our results imply that it is important to consider the symmetry of the tunneling couplings when constructing a charge sensor integrated QD device or qubit.

cond-mat.mes-hall↗

arXiv2021

A double quantum dot defined by top gates in a single crystalline InSb nanosheet

We report on the transport study of a double quantum dot (DQD) device made from a freestanding, single crystalline InSb nanosheet. The freestanding nanosheet is grown by molecular beam epitaxy and the DQD is defined by top gate technique. Through the transport measurements, we demonstrate how a single quantum dot (QD) and a DQD can be defined in an InSb nanosheet by tuning voltages applied to the top gates. We also measure the charge stability diagrams of the DQD and show that the charge states and the inter-dot coupling between the two individual QDs in the DQD can be efficiently regulated by the top gates. Numerical simulations for the potential profile and charge density distribution in the DQD have been performed and the results support the experimental findings and provide a better understanding of fabrication and transport characteristics of the DQD in the InSb nanosheet. The achieved DQD in the two-dimensional InSb nanosheet possesses pronounced benefits in lateral scaling and can thus serve as a new building block for developments of quantum computation and quantum simulation technologies.

cond-mat.mes-hall↗

arXiv2021

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↗

arXiv2020

Strong and tunable spin-orbit interaction in a single crystalline InSb nanosheet

A dual-gate InSb nanosheet field-effect device is realized and is used to investigate the physical origin and the controllability of the spin-orbit interaction in a narrow bandgap semiconductor InSb nanosheet. We demonstrate that by applying a voltage over the dual gate, efficiently tuning of the spin-orbit interaction in the InSb nanosheet can be achieved. We also find the presence of an intrinsic spin-orbit interaction in the InSb nanosheet at zero dual-gate voltage and identify its physical origin as a build-in asymmetry in the device layer structure. Having a strong and controllable spin-orbit interaction in an InSb nanosheet could simplify the design and realization of spintronic deceives, spin-based quantum devices and topological quantum devices.

cond-mat.mes-hall↗

arXiv2020

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 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 agreements in the charge stability diagrams of the TQD obtained by the direct transport measurements and by the charge-state transition detection measurements are 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 the three QDs in the TQD are close to be 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.

cond-mat.mes-hall↗

arXiv2020

In Situ Epitaxy of Pure Phase Ultra-Thin InAs-Al Nanowires for Quantum Devices

Hybrid semiconductor-superconductor InAs-Al nanowires with uniform and defect-free crystal interfaces are one of the most promising candidates used in the quest for Majorana zero modes (MZMs). However, InAs nanowires often exhibit a high density of randomly distributed twin defects and stacking faults, which result in an uncontrolled and non-uniform InAs-Al interface. Furthermore, this type of disorder can create potential inhomogeneity in the wire, destroy the topological gap, and form trivial sub-gap states mimicking MZM in transport experiments. Further study shows that reducing the InAs nanowire diameter from growth can significantly suppress the formation of these defects and stacking faults. Here, we demonstrate the in situ growth of ultra-thin InAs nanowires with epitaxial Al film by molecular-beam epitaxy. Our InAs diameter (~ 30 nm) is only one-third of the diameters (~ 100 nm) commonly used in literatures. The ultra-thin InAs nanowires are pure phase crystals for various different growth directions, suggesting a low level of disorder. Transmission electron microscopy confirms an atomically sharp and uniform interface between the Al shell and the InAs wire. Quantum transport study on these devices resolves a hard induced superconducting gap and $2e^-$ periodic Coulomb blockade at zero magnetic field, a necessary step for future MZM experiments. A large zero bias conductance peak with a peak height reaching 80% of $2e^2/h$ is observed.

cond-mat.mtrl-sci↗

arXiv2020

Measurements of spin-orbit interaction in epitaxially grown InAs nanosheets

We report on a low-temperature transport study of a single-gate, planar field-effect device made from a free-standing, wurtzite-crystalline InAs nanosheet. The nanosheet is grown via molecular beam epitaxy and the field-effect device is characterized by gate transfer characteristic measurements and by magnetic field orientation dependent transport measurements. The measurements show that the device exhibits excellent electrical properties and the electron transport in the nanosheet is of the two-dimensional nature. Low-field magnetoconductance measurements are performed for the device at different gate voltages and temperatures, and the characteristic transport lengths, such as phase coherent length, spin-orbit length and mean free path, in the nanosheet are extracted. It is found that the spin-orbit length in the nanosheet is short, on the order of 150 nm, demonstrating the presence of strong spin-orbit interaction in the InAs nanosheet. Our results show that epitaxially grown, free-standing, InAs nanosheets can serve as an emerging semiconductor nanostructure platform for applications in spintronics, spin qubits and planar topological quantum devices.

cond-mat.mes-hall↗

arXiv2020

Experimental free-space quantum secure direct communication and its security analysis

We report an experimental implementation of free-space quantum secure direct communication based on single photons. The quantum communication scheme uses phase encoding, and the asymmetric Mach-Zehnder interferometer is optimized so as to automatically compensate phase drift of the photons during their transitions over the free-space medium. An information transmission rate of 500 bps over a 10-meter free space with a mean quantum bit error rate of 0.49%$\pm$0.27% is achieved. The security is analyzed under the scenario that Eve performs collective attack and photon number splitting collective attack. Our results show that quantum secure direct communication is feasible in free space.

quant-ph↗

arXiv2018

Dimension Engineering of Narrow Bandgap Semiconductor InAs Nanostructures in Wafer-Scale

Here, we demonstrate an approach that provides a precise control of the dimension of InAs from one-dimensional nanowires to wafer-scale free-standing two-dimensional nanosheets, which have a high degree of crystallinity and outstanding electrical and optical properties, using molecular-beam epitaxy by controlling catalyst alloy segregation. In our approach, two-dimensional InAs nanosheets can be obtained directly from one-dimensional InAs nanowires by silver-indium alloy segregation, which is much easier than all previously reported method, such as traditional buffering technique and select area epitaxial growth. Detailed transmission electron microscopy investigations provide a solid evidence that the catalyst alloy segregation is the origination of the InAs dimensional transformation from one-dimensional nanowires to two-dimensional nanosheets, and even to three-dimensional complex crosses. Using this method, we find that the wafer-scale free-standing InAs nanosheets can be grown on various substrates including Si, MgO, sapphire and GaAs etc. The InAs nanosheets grown at high temperature are pure phase single crystals and have a high electron mobility and a long time-resolved THz kinetics lifetime. Our work will open up a conceptually new and general technology route toward the effective controlling the dimension of the low-dimensional III-V semiconductors. It may also enable the low-cost fabrication of free-standing nanosheet-based devices on an industrial scale.

cond-mat.mtrl-sci↗