Superconductors and semiconductors are crucial platforms in the field of quantum computing. They can be combined to hybrids, bringing together physical properties that enable the discovery of new emergent phenomena and provide novel strategies for quantum control. The involved semiconductor materials, however, suffer from disorder, hyperfine interactions or lack of planar technology. Here we realise an approach that overcomes these issues altogether and integrate gate-defined quantum dots and superconductivity into germanium heterostructures. In our system, heavy holes with mobilities exceeding 500,000 cm2 (Vs)−1 are confined in shallow quantum wells that are directly contacted by annealed aluminium leads. We observe proximity-induced superconductivity in the quantum well and demonstrate electric gate-control of the supercurrent. Germanium therefore has great promise for fast and coherent quantum hardware and, being compatible with standard manufacturing, could become a leading material for quantum information processing.
We investigate the magnetic field and temperature dependence of the single-electron spin lifetime in silicon quantum dots and find a lifetime of 2.8 ms at a temperature of 1.1 K. We develop a model based on spin-valley mixing and find that Johnson noise and two-phonon processes limit relaxation at low and high temperature respectively. We also investigate the effect of temperature on charge noise and find a linear dependence up to 4 K. These results contribute to the understanding of relaxation in silicon quantum dots and are promising for qubit operation at elevated temperatures.
We fabricate Josephson field-effect-transistors in germanium quantum wells contacted by superconducting aluminum and demonstrate supercurrents carried by holes that extend over junction lengths of several micrometers. In superconducting quantum point contacts we observe discretization of supercurrent, as well as Fabry-Perot resonances, demonstrating ballistic transport. The magnetic field dependence of the supercurrent follows a clear Fraunhofer-like pattern and Shapiro steps appear upon microwave irradiation. Multiple Andreev reflections give rise to conductance enhancement and evidence a transparent interface, confirmed by analyzing the excess current. These demonstrations of ballistic superconducting transport are promising for hybrid quantum technology in germanium.Quantum information processing in the solid-state is being pursued using superconducting and semiconducting platforms [1,2]. In both platforms, rudimentary quantum algorithms have already been demonstrated [3,4]. While decoherence is a central topic, advanced superconducting systems are now capable of entangling 10 qubits [5]. Spin qubits based on silicon (Si) and germanium (Ge), on the other hand, can be isotopically enriched to remove magnetic decoherence [6,7], resulting in extremely long coherence times [8,9]. Crucially, these qubits can be defined using conventional semiconductor technology. A hybrid approach may build upon the strengths of each platform motivating extensive research. Superconducting qubits with semiconductor elements have led to electric gate-tuneable superconducting qubits [10,11], or gatemons, while spin qubits interfaced with superconducting resonators have reached the regime of strong spin-photon coupling [12][13][14], an important step toward long-range entanglement.Hybrid technology in condensed matter physics has even more surprises and can host exotic excitations. In particular, a topological phase transition may occur in superconductor-semiconductor systems in the presence of spin-orbit coupling and magnetism [15,16]. At the topological transition, excitations emerge that represent Majorana fermion states that can exhibit non-Abelian exchange statistics. Next to their fundamental interest, these states are argued to be excellent building blocks for quantum computation as they bear some topological protection against decoherence. Despite protection limited only to operations inside the Clifford group, coupling topological qubits to spin qubits may offer an effective pathway toward universal quantum computation [17]. In addition, integrating topological systems to the spin qubit platform may enable the coupling of spatially separated spin qubits via topologically protected braiding operations [18,19].Germanium has the potential to become an excellent material platform for the construction of these hybrid systems. It can be isotopically purified, thereby removing decoherence by nuclear spins [6], and can host strong-spin orbit coupling [20], in particular when the charge carriers are holes. In addition, mobilities reach...
We present a novel reconfigurable metal-oxide-semiconductor multi-gate transistor that can host a quadruple quantum dot in silicon. The device consist of an industrial quadruple-gate silicon nanowire field-effect transistor. Exploiting the corner effect, we study the versatility of the structure in the single quantum dot and the serial double quantum dot regimes and extract the relevant capacitance parameters. We address the fabrication variability of the quadruple-gate approach which, paired with improved silicon fabrication techniques, makes the corner state quantum dot approach a promising candidate for a scalable quantum information architecture.Semiconductor quantum bits relying on the charge or spin degree of freedom of a single electron, bound to a quantum dot (QD) or impurity atom, are considered promising candidates for the base elements of solid state quantum computing architectures [1]. Building a successful quantum computer, however, requires a scalable multi-qubit approach to implement the necessary algorithms [2]. Electron spins bound to silicon QDs are seen as promising candidates for this due to their long coherence time, electrical tunability and flexible coupling geometries [3][4][5]. A further advantage of using Si is the possibility to integrate with current complementary-metaloxide-semiconductor (CMOS) technology [5-8] and leverage its established industrial platform for large scale circuits. Recently, the integration of Si quantum dots and double quantum dots (DQD) into CMOS technology has been taken a step further with reports of fewelectron QDs, DQDs, and donor-QD hybrids created within industry-standard Si nanowire transistors [9][10][11][12]. Combined with a gate-based readout scheme that alleviates the need for a separate charge sensor [10-14] these approaches pave the way towards a large scale quantum computing architecture based on current CMOS technology.In this Letter, we report on a reconfigurable QD and DQD system in a quadruple-gate CMOS transistor. It incorporates one, or a pair, of CMOS corner state quantum dots [10,11] in a variety of configurations. Each of the four gates can host an independently tunable quantum dot created in the square channel by electrostatic enhancement and confinement resulting from the topgate electrodes and accompanying silicon nitride spacers. We characterise one exemplary single QD and demonstrate that different DQD configurations can be set at will. Building on previous demonstrations [10][11][12] results provide a way to scale up CMOS quantum information architectures and to create reconfigurable silicon multi-dot arrangements. The device presented here is a fully depleted silicon-oninsulator (FDSOI) nanowire field-effect transistor with four independently addressable top-gates. The polyarXiv:1603.03636v1 [cond-mat.mes-hall]
We investigate the effect of the valley degree of freedom on Pauli-spin blockade readout of spin qubits in silicon. The valley splitting energy sets the singlet-triplet splitting and thereby constrains the detuning range. The valley phase difference controls the relative strength of the intra-and inter-valley tunnel couplings, which, in the proposed Pauli-spin blockade readout scheme, couple singlets and polarized triplets, respectively. We find that high-fidelity readout is possible for a wide range of phase differences, while taking into account experimentally observed valley splittings and tunnel couplings. We also show that the control of the valley splitting together with the optimization of the readout detuning can compensate the effect of the valley phase difference. To increase the measurement fidelity and extend the relaxation time we propose a latching protocol that requires a triple quantum dot and exploits weak long-range tunnel coupling. These opportunities are promising for scaling spin qubit systems and improving qubit readout fidelity. arXiv:1803.01811v1 [cond-mat.mes-hall]
We report on the valley blockade and the multielectron Kondo effect generated by an impurity atom in a silicon nano field effect device. According to the spin-valley nature of tunnelling processes, and consistently with those allowed by the valley blockade regime, the manifestation of Kondo effect obeys to the periodicity 4 of the electron filling sequence typical of silicon emerging at occupation N=1, 2, 3. The spin-valley Kondo effect emerges under different kinds of screening depending on the electron filling. By exploiting the valley blockade regime, valley index conservation in the Kondo SU(4) is deduced without the employment of an external magnetic field. Microwave irradiation suppresses the Kondo effect at occupancies up to three electrons.Comment: Paper structure reorganized with respect to v1. 14 pages, 16 figure
The development of quantum electronic devices operating below a few Kelvin degrees is raising the demand for cryogenic complementary metal-oxide-semiconductor electronics (CMOS) to be used as in situ classical control/readout circuitry. Having a minimal spatial separation between quantum and classical hardware is necessary to limit the electrical wiring to room temperature and the associated heat load and parasitic capacitances. Here, we report prototypical demonstrations of hybrid circuits combining silicon quantum dot devices and a classical transimpedance amplifier, which is characterized and then used to measure the current through the quantum dots. The two devices are positioned next to each other at 4.2 K to assess the use of the cryogenic transimpedance amplifier with respect to a room-temperature transimpedance amplifier. A quantum device built on the same substrate as the transimpedance amplifier is characterized down to 10 mK. The transimpedance amplifier is based on commercial 28 nm fully depleted Silicon-on-insulator (FDSOI) CMOS. It consists of a two-stage Miller-compensated operational amplifier with a 10 MΩ polysilicon feedback resistor, yielding a gain of 1.1×107 V/A. We show that the transimpedance amplifier operates at 10 mK with only 1 μW of power consumption, low enough to prevent heating. It exhibits linear response up to ±40 nA and a measurement bandwidth of 2.6 kHz, which could be extended to about 200 kHz by design optimization. The realization of custom-made electronics in FDSOI technology for cryogenic operation at any temperature will improve measurement speed and quality inside cryostats with higher bandwidth, lower noise, and higher signal-to-noise ratio.
We report on the development of a modular system of high-frequency printed circuit boards (PCBs) for electrical low-noise characterization of multigate quantum devices. The whole measurement setup comprises PCBs operating from room temperature to a few kelvins, and custom software to control the broadband electronics held at cryogenic and room temperature. The PCBs coupling scheme and the custom tailoring of the user panel make our platform particularly flexible. At the cryogenic stage, one board hosts the electronics for readout. It consists in a custom complementary metal-oxide-semiconductor circuit for the current sensing. It is composed by a multiplexer for a digital selection of the device under test among up to four samples, connected to a cryogenic transimpedance amplifier with two possible gains, the maximum bandwidth of 250 kHz and the minimum equivalent input noise of 10 fA/Hz. Such board is coupled to the PCB sample holder, where 14 low-frequency input lines bias the devices and control the gates. Four additional high-frequency input paths with a bandwidth of 1 GHz and an isolation lower than -40 dB at 3 GHz have been implemented to apply a few millivolt pulses with a minimum duration of 1 ns. The PCBs assemblage and the cryogenic electronics are electrically characterized at 4.2 K and later used to perform quantum transport spectroscopy and single-charge dynamics readout at a few microsecond scales in two silicon nanoscaled field-effect transistors
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.