arXiv subjects

Guo-Ping Guo

Publications and source records attributed to Guo-Ping Guo.

At least 163 records · Page 9Linked to original sources

arXiv2016

Charge Number Dependence of the Dephasing Rates of a Graphene Double Quantum Dot in a Circuit QED Architecture

We use an on-chip superconducting resonator as a sensitive meter to probe the properties of graphene double quantum dots at microwave frequencies. Specifically, we investigate the charge dephasing rates in a circuit quantum electrodynamics architecture. The dephasing rates strongly depend on the number of charges in the dots, and the variation has a period of four charges, over an extended range of charge numbers. Although the exact mechanism of this fourfold periodicity in dephasing rates is an open problem, our observations hint at the fourfold degeneracy expected in graphene from its spin and valley degrees of freedom.

cond-mat.mes-hall↗

arXiv2016

Strongly-coupled nanotube electromechanical resonators

Coupling an electromechanical resonator with carbon-nanotube quantum dots is a significant method to control both the electronic charge and the spin quantum states. By exploiting a novel micro-transfer technique, we fabricate two strongly-coupled and electrically-tunable mechanical resonators on a single carbon nanotube for the first time. The frequency of the two resonators can be individually tuned by the bottom gates, and strong coupling is observed between the electron charge and phonon modes of each resonator. Furthermore, the conductance of either resonator can be nonlocally modulated by the phonon modes in the other resonator. Strong coupling is observed between the phonon modes of the two resonators, which provides an effective long distance electron-electron interaction. The generation of phonon-mediated-spin entanglement is also theoretically analyzed for the two resonators. This strongly-coupled nanotube electromechanical resonator array provides an experimental platform for future studies of the coherent electron-phonon interaction, the phonon mediated long-distance electron interaction, and entanglement state generation.

cond-mat.mes-hall↗

arXiv2015

Suspending Effect on Low-Frequency Charge Noise in Graphene Quantum Dot

Charge noise is critical in the performance of gate-controlled quantum dots (QDs). Here we show the 1/f noise for a microscopic graphene QD is substantially larger than that for a macroscopic graphene field-effect transistor (FET), increasing linearly with temperature. To understand its origin, we suspended the graphene QD above the substrate. In contrast to large area graphene FETs, we find that a suspended graphene QD has an almost-identical noise level as an unsuspended one. Tracking noise levels around the Coulomb blockade peak as a function of gate voltage yields potential fluctuations of order 1 "μeV", almost one order larger than in GaAs/GaAlAs QDs. Edge states rather than substrate-induced disorders, appear to dominate the 1/f noise, thus affecting the coherency of graphene nano-devices.

cond-mat.mes-hall↗

arXiv2015

Temperature dependence of Coulomb oscillations in a few-layer two-dimensional WS2 quantum dot

Standard semiconductor fabrication techniques are used to fabricate a quantum dot (QD) made of WS2, where Coulomb oscillations were found. The full-width-at-half-maximum of the Coulomb peaks increases linearly with temperature while the height of the peaks remains almost independent of temperature, which is consistent with standard semiconductor QD theory. Unlike graphene etched QDs, where Coulomb peaks belonging to the same QD can have different temperature dependences, these results indicate the absence of the disordered confining potential. This difference in the potential-forming mechanism between graphene etched QDs and WS2 QDs may be the reason for the larger potential fluctuation found in graphene QDs.

cond-mat.mes-hall↗

arXiv2015

A gate defined quantum dot on the two-dimensional transition metal dichalcogenide semiconductor WSe2

Two-dimensional layered materials, such as transition metal dichalcogenides (TMDCs), are promising materials for future electronics owing to their unique electronic properties. With the presence of a band gap, atomically thin gate defined quantum dots (QDs) can be achieved on TMDCs. Here, standard semiconductor fabrication techniques are used to demonstrate quantum confined structures on WSe2 with tunnel barriers defined by electric fields, thereby eliminating the edge states induced by etching steps, which commonly appear in gapless graphene QDs. Over 40 consecutive Coulomb diamonds with a charging energy of approximately 2 meV were observed, showing the formation of a QD, which is consistent with the simulations. The size of the QD could be tuned over a factor of 2 by changing the voltages applied to the top gates. These results shed light on quantum nano-devices on TMDCs for further researches.

cond-mat.mes-hall↗

arXiv2015

Transmission of Photonic Quantum Polarization Entanglement in a Nanoscale Hybrid Plasmonic Waveguide

Photonic quantum technologies have been extensively studied in quantum information science, owing to the high-speed transmission and outstanding low-noise properties of photons. However, applications based on photonic entanglement are restricted due to the diffraction limit. In this work, we demonstrate for the first time the maintaining of quantum polarization entanglement in a nanoscale hybrid plasmonic waveguide composed of a fiber taper and a silver nanowire. The transmitted state throughout the waveguide has a fidelity of 0.932 with the maximally polarization entangled state Φ+. Furthermore, the Clauser, Horne, Shimony, and Holt (CHSH) inequality test performed, resulting in value of 2.495+/-0.147 > 2, demonstrates the violation of the hidden variable model. Because the plasmonic waveguide confines the effective mode area to subwavelength scale, it can bridge nanophotonics and quantum optics and may be used as near-field quantum probe in a quantum near-field micro/nanoscope, which can realize high spatial resolution, ultrasensitive, fiber-integrated, and plasmon-enhanced detection.

quant-ph↗

arXiv2014

Introduction of DC line structures into a superconducting microwave 3D cavity

We report a technique that can noninvasively add multiple DC wires into a 3D superconducting microwave cavity for electronic devices that require DC electrical terminals. We studied the influence of our DC lines on the cavity performance systematically. We found that the quality factor of the cavity is reduced if any of the components of the electrical wires cross the cavity equipotential planes. Using this technique, we were able to incorporate a quantum dot (QD) device into a 3D cavity. We then controlled and measured the QD transport signal using the DC lines. We have also studied the heating effects of the QD by the microwave photons in the cavity.

cond-mat.mes-hall↗

arXiv2014

Controlled-Not Quantum Logic Gate in Two Strongly Coupled Semiconductor Charge Qubits

A crucial requirement for scalable quantum-information processing is the realization of multiple-qubit quantum gates. Universal multiple-qubit gates can be implemented by a set of universal single qubit gates and any one kind of two-qubit gate, such as a controlled-NOT (CNOT) gate. Semiconductor quantum dot qubits are a leading approach for the physical implementation of quantum computation, due to their potential for large-scale integration. Two-qubit gate operations have been so far only demonstrated in individual electron spin-based quantum dot systems. Due to the relatively short de-coherence time, charge qubits in quantum dots are generally considered to be inferior for going beyond single qubit level. Here, we demonstrate the benchmarking CNOT gate in two capacitively coupled charge qubits, each consisting of an electron confined in a GaAs/AlGaAs double quantum dot. Owing to the strong inter-qubit coupling strength, gate operations with a clock speed up to 5GHz has been realized. A processing tomography shows encouragingly that the universal two-qubit gate operations have comparable fidelities to that of spin-based two-qubit gates. Our results suggest that semiconductor charge qubits have a considerable potential for scalable quantum computing and may stimulate the use of long-range Coulomb interaction for coherent quantum control in other devices.

quant-ph↗

arXiv2014

Two-dimensional superconductivity at (110) LaAlO3/SrTiO3 interfaces

Novel low dimensional quantum phenomena are expected at (110) LaAlO3/SrTiO3 (LAO/STO) interfaces after the quasi two dimensional electron gas similar to that of (001) LAO/STO interfaces was found [G. Herranz et al., Sci. Rep. 2, 758 (2012) and A. Annadi et al., Nat. Commun. 4, 1838 (2013)]. Here, two dimensional superconductivity of (110) LAO/STO samples with a superconducting transition temperature of 184 mK is demonstrated based on systematical transport measurements. The two dimensional characteristic of the superconductivity is confirmed by analyzing the Berezinskii-Kosterlitz-Thouless transition. The estimated superconductive thickness is about 18 nm. These features of superconductivity of (110) LAO/STO interfaces are comparable to those of (001) LAO/STO interfaces. This discovery may inspire a new round of upsurge on study of LAO/STO interfaces.

cond-mat.supr-con↗

arXiv2014

Coupling two distant double quantum dots to a microwave resonator

With recent advances in the circuit quantum electrodynamics (cQED) architecture, hybrid systems that couple nano-devices to microwave resonators have been developing rapidly. Here we report an experimental demonstration of two graphene double quantum dots (DQDs) coupled over a distance of up to 60 μm, through a microwave resonator. We jointly measure the two DQDs' coupling to the resonator, which causes a nonlinear response in the resonator reflection amplitude in the vicinity of the degeneracy points of the two DQDs. This phenomenon is explained by the Tavis-Cummings (T-C) mode. We further characterize this nonlocal coupling by measuring the correlation between the DC currents in the two DQDs. This correlation is observed to be strongly dependent on the average photon number in the resonator. Our results explore T-C physics in electronic transport, and also contribute to the study of nonlocal transport and future implementations of remote electronic entanglement.

cond-mat.mes-hall↗

arXiv2014

Fabrication and characterization of an undoped GaAs/AlGaAs quantum dot device

We demonstrate the development of a double quantum dot with an integrated charge sensor fabricated in undoped GaAs/AlGaAs heterostructures using a double top-gated design. Based on the evaluation of the integrated charge sensor, the double quantum dot can be tuned to a few-electron region. Additionally, the inter-dot coupling of the double quantum dot can be tuned to a large extent according to the voltage on the middle gate. The quantum dot is shown to be tunable from a single dot to a well-isolated double dot. To assess the stability of such design, the potential fluctuation induced by 1/f noise was measured. Based on the findings herein, the quantum dot design developed in the undoped GaAs/AlGaAs semiconductor shows potential for the future exploitation of nano-devices.

cond-mat.mes-hall↗

arXiv2014

High visibility on-chip quantum interference of single surface plasmons

Quantum photonic integrated circuits (QPICs) based on dielectric waveguides have been widely used in linear optical quantum computation. Recently, surface plasmons have been introduced to this application because they can confine and manipulate light beyond the diffraction limit. In this study, the on-chip quantum interference of two single surface plasmons was achieved using dielectric-loaded surface-plasmon-polariton waveguides. The high visibility (greater than 90%) proves the bosonic nature of single plasmons and emphasizes the feasibility of achieving basic quantum logic gates for linear optical quantum computation. The effect of intrinsic losses in plasmonic waveguides with regard to quantum information processing is also discussed. Although the influence of this effect was negligible in the current experiment, our studies reveal that such losses can dramatically reduce quantum interference visibility in certain cases; thus, quantum coherence must be carefully considered when designing QPIC devices.

quant-ph↗

arXiv2013

Observation of Kondo Effect in a Quadruple Quantum Dots

We investigate the Kondo effect in a quadruple quantum dot device of coupled-double quantum dots (DQDs), which simultaneously contains intra-DQDs and inter-DQDs coupling. A variety of novel behaviors are observed. The differential conductance dI/dV is measured in the upper DQDs as a function of source drain bias. It is found to exhibit multiple peaks, including a zero-bias peak, where the number of peaks exceeds five. Alternatively, tuning the lower DQDs yielded regions of four peaks. In addition, a Kondo-effect switcher is demonstrated, using the lower DQDs as the controller.

cond-mat.mes-hall↗

arXiv2013

Symmetric reflection line resonator for semiconductor circuit quantum electrodynamics

We have designed and fabricated a half-wavelength reflection line resonator (RLR) that consists of a pair of two coupled microstrip lines on a GaAs/AlGaAs heterostructure. By changing the top gate voltage on a square of two dimensional electron gas under the resonator, a large range of the quality factors can be obtained. Energy loss in the two-dimensional electron gas can be minimized, thus realizing a versatile resonator suitable for integration with semiconductor quantum circuits.

cond-mat.mes-hall↗

arXiv2013

Photon-assisted-tunneling in a coupled double quantum dot out of thermal equilibrium

We perform photon-assisted-tunneling (PAT) experiments on a GaAs double quantum dot device under high microwave excitation power. Photon-assisted absorption of up to 14 photons is observed, when electron temperature (>1K) are far above the lattice temperature. Signatures of Landau-Zener-Stückelberg (LZS) interference are found even in this non-equilibrium PAT spectrum. In addition, the charge state relaxation time T_1~8ns measured in this out of thermal equilibrium double quantum dot is in agreement with other previous reports.

cond-mat.mes-hall↗

arXiv2013

Detecting orbital angular momentum through division-of-amplitude interference with a circular plasmonic lens

We demonstrate a novel detection scheme for the orbital angular momentum (OAM) of light using circular plasmonic lens. Owing to a division-of-amplitude interference phenomenon between the surface plasmon waves and directly transmitted light, specific intensity distributions are formed near the plasmonic lens surface under different OAM excitations. Due to different phase behaviors of the evanescent surface plasmon wave and the direct transmission, interference patterns rotate as the observation plane moves away from the lens surface. The rotation direction is a direct measure of the sign of OAM, while the amount of rotation is linked to the absolute value of the OAM. This OAM detection scheme is validated experimentally and numerically. Analytical expressions are derived to provide insights and explanations of this detection scheme. This work forms the basis for the realization of a compact and integrated OAM detection architect that may significantly benefit optical information processing with OAM states.

physics.optics↗

arXiv2013

Tuning inter-dot tunnel coupling of an etched graphene double quantum dot by adjacent metal gates

Graphene double quantum open the possibility to use charge or spin degrees of freedom for storing and manipulating quantum information in this new electronic material. However, impurities and edge disorders in etched graphene nano-structures hinder the ability to control the inter-dot tunnel coupling, tc,the most important property of the artificial molecule. Here we report measurements of tc in an all-metal-gates-tuned graphene DQD. We find that tc can be controlled continuously about a factor of four by employing a single gate. Furthermore, tc, can be changed monotonically about another factor of four as electrons are gate-pumped into the dot one by one. The results suggest that the strength of tunnel coupling in etched DQDs can be varied in a rather broad range and in a controllable manner, which improves the outlook to use graphene as a base material for qubit applications.

cond-mat.mes-hall↗

arXiv2013

Quantum simulation of Kibble-Zurek mechanism with a semiconductor electron charge qubit

The Kibble-Zurek mechanism provides a description of the topological structure occurring in the symmetry breaking phase transitions, which may manifest as the cosmological strings in the early universe or vortex lines in the superfulid. A particularly intriguing analogy between Kibble-Zurek mechanism and a text book quantum phenomenon, Landau-Zener transition has been discovered, but is difficult to observe up to now. In recent years, there has been broad interest in quantum simulations using different well-controlled physical setups, in which full tunability allows access to unexplored parameter regimes. Here we demonstrate a proof-of-principle quantum simulation of Kibble-Zurek mechanism using a single electron charge qubit in double quantum dot, set to behave as Landau-Zener dynamics. We measure the qubit states as a function of driven pulse velocity and successfully reproduce Kibble-Zurek like dependence of topological defect density on the quench rate. The high-level controllability of semiconductor two-level system make it a platform to test the key elements of topological defect formation process and shed a new insight on the aspect of non-equilibrium phase transitions.

quant-ph↗