arXiv subjects

V. F. Maisi

Publications and source records attributed to V. F. Maisi.

At least 19 recordsLinked to original sources

arXiv2026

Photonic Mode Description of the Jaynes-Cummings Hamiltonian States

Jaynes-Cummings Hamiltonian provides the elemental description of a two-level system interacting with a photonic mode. In this work, we review the Jaynes-Cummings formalism for an electronic two-level system. The purpose is to summarize and connect together the key theory concepts relevant for the transmission response probed typically in the experiments. The review provides a photonic mode description of the response with analytical results for several limiting cases. These expressions are useful for gaining understanding and intuition on what influences the measured response. We also connect the photonic response to several key concepts in the field: the dispersive shift in qubit readout, the quantum capacitance of semiconductor nanostructures and the effective dissipation rate of the two-level system.

quant-ph↗

arXiv2024

Hot Carrier Nanowire Transistors at the Ballistic Limit

We demonstrate experimentally non-equilibrium transport in unipolar quasi-1D hot electron devices reaching ballistic limit. The devices are realized with heterostructure engineering in nanowires to obtain dopant- and dislocation-free 1D-epitaxy and flexible bandgap engineering. We show experimentally the control of hot electron injection with a graded conduction band profile and subsequent filtering of hot and relaxed electrons with rectangular energy barriers. The number of electron passing the barrier depends exponentially on the transport length with a mean free path of 200 - 260 nm and reaches ballistic transport regime for the shortest devices with 70 % of the electrons flying freely through the base electrode and the barrier reflections limiting the transport to the collector.

cond-mat.mes-hall↗

arXiv2024

High-Impedance Microwave Resonators with Two-Photon Nonlinear Effects

In this article, we present an experimental study of a Josephson junction -based high-impedance resonator. By taking the resonator to the limit of consisting effectively only of one junction, results in strong non-linear effects already for the second photon while maintaining a high impedance of the resonance mode. Our experiment yields thus resonators with the strong interactions both between individual resonator photons and from the resonator photons to other electric quantum systems. We also present an energy diagram technique which enables to measure, identify and analyse different multi-photon optics processes along their energy conservation lines.

quant-ph↗

arXiv2022

A superconductor free of quasiparticles for seconds

Superconducting devices, based on the Cooper pairing of electrons, play an important role in existing and emergent technologies, ranging from radiation detectors to quantum computers. Their performance is limited by spurious quasiparticle excitations formed from broken Cooper pairs. Efforts to achieve ultra-low quasiparticle densities have reached time-averaged numbers of excitations on the order of one in state-of-the-art devices. However, the dynamics of the quasiparticle population as well as the time scales for adding and removing individual excitations remain largely unexplored. Here, we experimentally demonstrate a superconductor completely free of quasiparticles for periods lasting up to seconds. We monitor the quasiparticle number on a mesoscopic superconductor in real time by measuring the charge tunneling to a normal metal contact. Quiet, excitation-free periods are interrupted by random-in-time Cooper pair breaking events, followed by a burst of charge tunneling within a millisecond. Our results demonstrate the possibility of operating devices without quasiparticles with potentially improved performance. In addition, our experiment probes the origins of nonequilibrium quasiparticles in our device; the decay of the Cooper pair breaking rate over several weeks following the initial cooldown rules out processes arising from cosmic or long-lived radioactive sources.

cond-mat.supr-con↗

arXiv2022

Electrostatic control of quasiparticle poisoning in a hybrid semiconductor-superconductor island

The performance of superconducting devices is often degraded by the uncontrolled appearance and disappearance of quasiparticles, a process known as poisoning. We demonstrate electrostatic control of quasiparticle poisoning in the form of single-charge tunneling across a fixed barrier onto a Coulomb island in an InAs/Al hybrid nanowire. High-bandwidth charge sensing was used to monitor charge occupancy of the island across Coulomb blockade peaks, where tunneling rates were maximal, and Coulomb valleys, where tunneling was absent. Electrostatic gates changed on-peak tunneling rates by two orders of magnitude for a barrier with fixed normal-state resistance, which we attribute to gate dependence of the size and softness of the induced superconducting gap on the island, corroborated by separate density-of-states measurements. Temperature and magnetic field dependence of tunneling rates are also investigated.

cond-mat.mes-hall↗

arXiv2021

A self-calibrating superconducting pair-breaking detector

We propose and experimentally demonstrate a self-calibrating detector of Cooper pair depairing in a superconductor based on a mesoscopic superconducting island coupled to normal metal leads. On average, exactly one electron passes through the device per broken Cooper pair, independent of the absorber volume, device or material parameters. The device operation is explained by a simple analytical model and verified with numerical simulations in quantitative agreement with experiment. In a proof-of-concept experiment, we use such a detector to measure the high-frequency phonons generated by another, electrically decoupled superconducting island, with a measurable signal resulting from less than 10 fW of dissipated power.

cond-mat.supr-con↗

arXiv2021

Quantum confinement suppressing electronic heat flow below the Wiedemann-Franz law

The Wiedemann-Franz law states that the charge conductance and the electronic contribution to the heat conductance are proportional. This sets stringent constraints on efficiency bounds for thermoelectric applications, which seek for large charge conduction in response to a small heat flow. We present experiments based on a quantum dot formed inside a semiconducting InAs nanowire transistor, in which the heat conduction can be tuned significantly below the Wiedemann-Franz prediction. Comparison with scattering theory shows that this is caused by quantum confinement and the resulting energy-selective transport properties of the quantum dot. Our results open up perspectives for tailoring independently the heat and electrical conduction properties in semiconductor nanostructures.

cond-mat.mes-hall↗

arXiv2020

Ambipolar Transport in Narrow Bandgap Semiconductor InSb Nanowires

We report on transport measurement study of top-gated field effect transistors made out of InSb nanowires grown by chemical vapor deposition. The transistors exhibit ambipolar transport characteristics revealed by three distinguished gate-voltage regions: In the middle region where the fermi level resides within the bandgap, the electrical resistance shows an exponential dependence on temperature and gate voltage. With either more positive or negative gate voltages, the devices enter the electron and hole transport regimes, revealed by a resistance decreasing linearly with decreasing temperature. From the transport measurement data of a 1-$μ$m-long device made from a nanowire of 50 nm in diameter, we extract a bandgap energy of 190-220 meV. The off-state current of this device is found to be suppressed within the measurement noise at a temperature of T = 4 K. A shorter, 260-nm-long device is found to exhibit a finite off-state current and a hole, on-state, circumference-normalized current of 11 $μ$A/$μ$m at V$_D$ = 50 mV which is the highest for such a device to our knowledge. The ambipolar transport characteristics make the InSb nanowires attractive for CMOS electronics, hybrid electron-hole quantum systems and hole based spin qubits.

cond-mat.mes-hall↗

arXiv2019

Detecting parity effect in a superconducting device in the presence of parity switches

We present a superconducting device showing a clear parity effect in the number of electrons, even when there is, on average, a single nonequilibrium quasiparticle present and the parity of the island switches due to quasiparticles tunneling in and out of the device at rates on the order of 100 Hz. We detect the switching by monitoring in real time the charge state of a superconducting island connected to normal leads by tunnel junctions. The quasiparticles are created by Cooper pairs breaking on the island at a rate of a few kHz. We demonstrate that the pair breaking is caused by the backaction of the single-electron transistor used as a charge detector. With sufficiently low probing currents, our superconducting island is free of quasiparticles 97% of the time.

cond-mat.mes-hall↗

arXiv2019

Coulomb Blockade from the Shell of an InP-InAs Core-Shell Nanowire with a Triangular Cross Section

We report on growth of InP-InAs core-shell nanowires and demonstration of the formation of single quantum structures, which show Coulomb blockade effect, over entire lengths of the nanowires. The core-shell nanowires are grown by a selective area growth technique via metal-organic vapor phase epitaxy. The as-grown core-shell nanowires are found to be of wurtzite crystals. The InP cores have a hexagonal cross section, while the InAs shell are grown preferentially on specific {1$\bar{1}$00} facets, leading to the formation of the core-shell nanowires with an overall triangular cross section. The grown core-shell nanowires are transferred on to a Si/SiO$_2$ substrate and then contacted with several narrow metal electrodes. Low-temperature transport measurements show the Coulomb-blockade effect. We analyze the measured gate capacitance and single electron charging energy of the devices and demonstrate that a quantum structure which shows the Coulomb blockade effect of a many-electron quantum dot is formed over the full length of a single core-shell nanowire and consists of the entire InAs shell in the nanowire.

cond-mat.mes-hall↗

arXiv2017

Hybrid single-electron turnstiles with thick superconducting electrodes for improved quasiparticle relaxation

We demonstrate shadow evaporation-based fabrication of high-quality ultrasmall normal metal -- insulator -- superconductor tunnel junctions where the thickness of the superconducting electrode is not limited by the requirement of small junction size. The junctions are formed between a film of manganese-doped aluminium acting as the normal conducting electrode, covered by a thicker, superconducting layer of pure Al. We characterize the junctions by sub-gap current--voltage measurements and charge pumping measurements in a gate-driven hybrid single-electron transistor, operated as a turnstile for single electrons. The technique allows to advance towards turnstiles with close to ideally thermalized superconducting reservoirs, prerequisite for reaching metrological current quantization accuracy in a hybrid turnstile. We further present an alternative way to realize small junctions with thick Al leads based on multi-angle deposition. The work enables the future investigation of turnstiles based on superconductors other than Al, and benefits various other Al tunnel junction devices for which quasiparticle thermalization is essential.

cond-mat.mes-hall↗

arXiv2016

InAs nanowire with epitaxial aluminium as a single-electron transistor with fixed tunnel barriers

We report on fabrication of single-electron transistors using InAs nanowires with epitaxial aluminium with fixed tunnel barriers made of aluminium oxide. The devices exhibit a hard superconducting gap induced by the proximized aluminium cover shell and they behave as metallic single-electron transistors. In contrast to the typical few channel contacts in semiconducting devices, our approach forms opaque multichannel contacts to a semiconducting wire and thus provides a complementary way to study them. In addition, we confirm that unwanted extra quantum dots can appear at the surface of the nanowire. Their presence is prevented in our devices, and also by inserting a protective layer of GaAs between the InAs and Al, the latter being suitable for standard measurement methods.

cond-mat.mes-hall↗

arXiv2015

Spin orbit coupling at the level of a single electron

We utilize electron counting techniques to distinguish a spin conserving fast tunneling process and a slower process involving spin flips in AlGaAs/GaAs-based double quantum dots. By studying the dependence of the rates on the interdot tunnel coupling of the two dots, we find that as many as 4% of the tunneling events occur with a spin flip related to spin-orbit coupling in GaAs. Our measurement has a fidelity of 99 % in terms of resolving whether a tunneling event occurred with a spin flip or not.

cond-mat.mes-hall↗

arXiv2015

On-chip error counting for hybrid metallic single-electron turnstiles

We perform in-situ detection of individual electrons pumped through a single-electron turnstile based on ultrasmall normal metal - insulator - superconductor tunnel junctions. In our setup, limited by the detector bandwidth, at low repetition rates we observe errorless sequential transfer of up to several hundred electrons through the system. At faster pumping speeds up to 100 kHz, we show relative error rates down to 10^-3, comparable to typical values obtained from measurements of average pumped current in non-optimized individual turnstiles. The work constitutes an initial step towards a self-referenced current standard realized with metallic single-electron turnstiles, complementing approaches based on semiconductor quantum dot pumps. It is the first demonstration of on-chip pumping error detection at operation frequencies exceeding the detector bandwidth, in a configuration where the average pumped current can be simultaneously measured. The scheme in which electrons are counted from the superconducting lead of the turnstile, instead of direct probing of the normal metal island, also enables studies of fundamental higher-order tunneling processes in the hybrid structures, previously not in reach with simpler configurations.

cond-mat.mes-hall↗

arXiv2015

Microwave Emission from Hybridized States in a Semiconductor Charge Qubit

We explore the microwave radiation emitted from a biased double quantum dot due to the inelastic tunneling of single charges. Radiation is detected over a broad range of detuning configurations between the dot energy levels with pronounced maxima occurring in resonance with a capacitively coupled transmission line resonator. The power emitted for forward and reverse resonant detuning is found to be in good agreement with a rate equation model, which considers the hybridization of the individual dot charge states.

cond-mat.mes-hall↗

arXiv2015

Interplay of charge and vorticity quantization in superconducting Coulomb blockaded island

The angular momentum or vorticity of Cooper pairs is shown to affect strongly the charge transfer through a small superconducting (S) island of a single electron transistor. This interplay of charge and rotational degrees of freedom in a mesoscopic superconductor occurs through the effect of vorticity on the quantum mechanical spectrum of electron-hole excitations. The subgap quasiparticle levels in vortices can host an additional electron, thus, suppressing the so-called parity effect in the S island. We propose to measure this interaction between the quantized vorticity and electric charge via the charge pumping effect caused by alternating vortex entry and exit controlled by a periodic magnetic field.

cond-mat.supr-con↗

arXiv2014

Characterization of aluminum oxide tunnel barriers by combining transport measurements and transmission electron microscope imaging

We present two approaches for studying the uniformity of a tunnel barrier. The first approach is based on measuring single-electron and two-electron tunneling in a hybrid single-electron transistor. Our measurements indicate that the effective area of a conduction channel is about one order of magnitude larger than predicted by theoretical calculations. With the second method, transmission electron microscopy, we demonstrate that variations in the barrier thickness are a plausible explanation for the larger effective area and an enhancement of higher order tunneling processes.

cond-mat.mes-hall↗

arXiv2014

Experimental realization of a Szilard engine with a single electron

The most succinct manifestation of the second law of thermodynamics is the limitation the Landauer principle imposes on the amount of heat a Maxwell demon (MD) can convert into free energy per single bit of information obtained in a measurement. We suggest and experimentally realize a reversible electronic MD based on a single-electron box operated as a Szilard engine, providing the first demonstration of this limitation: extraction of kT ln 2 of heat from the reservoir at temperature T per one bit of created information. The information is encoded in the position of an extra electron in the box.

cond-mat.mes-hall↗