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result(s) for
"Collard, Patrick"
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Coherent Spin-Spin Coupling Mediated by Virtual Microwave Photons
We report the coherent coupling of two electron spins at a distance via virtual microwave photons. Each spin is trapped in a silicon double quantum dot at either end of a superconducting resonator, achieving spin-photon couplings up to aroundgs/2π=40MHz. As the two spins are brought into resonance with each other, but detuned from the photons, an avoided crossing larger than the spin linewidths is observed with an exchange splitting around2J/2π=20MHz. In addition, photon-number states are resolved from the shift2χs/2π=−13MHzthat they induce on the spin frequency. These observations demonstrate that we reach the strong dispersive regime of circuit quantum electrodynamics with spins. Achieving spin-spin coupling without real photons is essential to long-range two-qubit gates between spin qubits and scalable networks of spin qubits on a chip.
Journal Article
A silicon metal-oxide-semiconductor electron spin-orbit qubit
The silicon metal-oxide-semiconductor (MOS) material system is a technologically important implementation of spin-based quantum information processing. However, the MOS interface is imperfect leading to concerns about 1/
f
trap noise and variability in the electron
g
-factor due to spin–orbit (SO) effects. Here we advantageously use interface–SO coupling for a critical control axis in a double-quantum-dot singlet–triplet qubit. The magnetic field-orientation dependence of the
g
-factors is consistent with Rashba and Dresselhaus interface–SO contributions. The resulting all-electrical, two-axis control is also used to probe the MOS interface noise. The measured inhomogeneous dephasing time,
T
2m
⋆
, of 1.6 μs is consistent with 99.95%
28
Si enrichment. Furthermore, when tuned to be sensitive to exchange fluctuations, a quasi-static charge noise detuning variance of 2 μeV is observed, competitive with low-noise reports in other semiconductor qubits. This work, therefore, demonstrates that the MOS interface inherently provides properties for two-axis qubit control, while not increasing noise relative to other material choices.
As the performance of silicon-based qubits has improved, there has been increasing focus on developing designs that are compatible with industrial processes. Here, Jock et al. exploit spin-orbit coupling to demonstrate full, all-electrical control of a metal-oxide-semiconductor electron spin qubit.
Journal Article
High-Fidelity Single-Shot Readout for a Spin Qubit via an Enhanced Latching Mechanism
The readout of semiconductor spin qubits based on spin blockade is fast but suffers from a small charge signal. Previous work suggested large benefits from additional charge mapping processes; however, uncertainties remain about the underlying mechanisms and achievable fidelity. In this work, we study the single-shot fidelity and limiting mechanisms for two variations of an enhanced latching readout. We achieve average single-shot readout fidelities greater than 99.3% and 99.86% for the conventional and enhanced readout, respectively, the latter being the highest to date for spin blockade. The signal amplitude is enhanced to a full one-electron signal while preserving the readout speed. Furthermore, layout constraints are relaxed because the charge sensor signal is no longer dependent on being aligned with the conventional (2,0)–(1,1) charge dipole. Silicon donor-quantum-dot qubits are used for this study, for which the dipole insensitivity substantially relaxes donor placement requirements. One of the readout variations also benefits from a parametric lifetime enhancement by replacing the spin-relaxation process with a charge-metastable one. This provides opportunities to further increase the fidelity. The relaxation mechanisms in the different regimes are investigated. This work demonstrates a readout that is fast, has a one-electron signal, and results in higher fidelity. It further predicts that going beyond 99.9% fidelity in a few microseconds of measurement time is within reach.
Journal Article
Coherent coupling between a quantum dot and a donor in silicon
Individual donors in silicon chips are used as quantum bits with extremely low error rates. However, physical realizations have been limited to one donor because their atomic size causes fabrication challenges. Quantum dot qubits, in contrast, are highly adjustable using electrical gate voltages. This adjustability could be leveraged to deterministically couple donors to quantum dots in arrays of qubits. In this work, we demonstrate the coherent interaction of a
31
P donor electron with the electron of a metal-oxide-semiconductor quantum dot. We form a logical qubit encoded in the spin singlet and triplet states of the two-electron system. We show that the donor nuclear spin drives coherent rotations between the electronic qubit states through the contact hyperfine interaction. This provides every key element for compact two-electron spin qubits requiring only a single dot and no additional magnetic field gradients, as well as a means to interact with the nuclear spin qubit.
In silicon, quantum information can be stored in donors or quantum dots, each with its advantages and limitations—particularly in terms of fabrication. Here the authors coherently couple a phosphorous donor’s electron spin to a quantum dot, encoding information in the hybrid two-electron system’s state.
Journal Article
Impact of interface traps on charge noise and low-density transport properties in Ge/SiGe heterostructures
Hole spins in Ge/SiGe heterostructures have emerged as an interesting qubit platform with favourable properties such as fast electrical control and noise-resilient operation at sweet spots. However, commonly observed gate-induced electrostatic disorder, drifts, and hysteresis hinder reproducible tune-up of SiGe-based quantum dot arrays. Here, we study Hall bar and quantum dot devices fabricated on Ge/SiGe heterostructures and present a consistent model for the origin of gate hysteresis and its impact on transport metrics and charge noise. As we push the accumulation voltages more negative, we observe non-monotonous changes in the low-density transport metrics, attributed to the induced gradual filling of a spatially varying density of charge traps at the SiGe-oxide interface. With each gate voltage push, we find local activation of a transient low-frequency charge noise component that completely vanishes again after 30 hours. Our results highlight the resilience of the SiGe material platform to interface-trap-induced disorder and noise and pave the way for reproducible tuning of larger multi-dot systems.Hole spins in SiGe quantum dot arrays are a promising qubit platform, but suffer from gate-induced electrostatic disorder, drift and hysteresis. Here, Hall bar and quantum dot Ge/SiGe heterostructures are studied, obtaining a model for gate hysteresis and its effect on transport and charge noise.
Journal Article
Cavity-mediated iSWAP oscillations between distant spins
Direct interactions between quantum particles naturally fall off with distance. However, future quantum computing architectures are likely to require interaction mechanisms between qubits across a range of length scales. In this work, we demonstrate a coherent interaction between two semiconductor spin qubits 250 μm apart using a superconducting resonator. This separation is several orders of magnitude larger than for the commonly used direct interaction mechanisms in this platform. We operate the system in a regime in which the resonator mediates a spin–spin coupling through virtual photons. We report the anti-phase oscillations of the populations of the two spins with controllable frequency. The observations are consistent with iSWAP oscillations of the spin qubits, and suggest that entangling operations are possible in 10 ns. These results hold promise for scalable networks of spin qubit modules on a chip.
Coupling semiconductor spin qubits over long distances using a superconducting resonator makes different quantum architectures possible. Now, the coherent swapping of quantum states has been observed between qubits coupled using this design.
Journal Article
Oro y hambre en la primera Década de Pedro Mártir de Anglería
Chapters 4 and 5 of the first
Decade
, devoted to the four voyages (1492–1504) of Columbus, from the
De orbe novo decades octo
centre around the battle against hunger and its connection with the search for gold. Especially striking is the story of a famine which was caused by the natives themselves on the island Hispaniola as an ultimate weapon against the military superiority of the Spaniards, convinced as they were that only physical hunger among the intruders could be stronger than their hunger for gold. The author emphasises the measures taken by the Columbus brothers to meet the need for food. No less striking, from a narratological as well as a thematic perspective, are the references to cannibalism. In the information provided by the natives the cannibals indeed appear to be the frightening guardians of the place where gold is to be found. The last chapter deals with the victory of abundance over hunger. It contains an idyllic-propagandist description of the coming into existence of the colonial society on Hispaniola, by the import of metropolitan products, which are more profitable in the New World than in the Old one.
Journal Article
A Fabrication Process for Emerging Nanoelectronic Devices Based on Oxide Tunnel Junctions
We present a versatile nanodamascene process for the realization of low-power nanoelectronic devices with different oxide junctions. With this process we have fabricated metal/insulator/metal junctions, metallic single electron transistors, silicon tunnel field effect transistors, and planar resistive memories. These devices do exploit one or two nanometric-scale tunnel oxide junctions based on TiO2, SiO2, HfO2, Al2O3, or a combination of those. Because the nanodamascene technology involves processing temperatures lower than 300°C, this technology is fully compatible with CMOS back-end-of-line and is used for monolithic 3D integration.
Journal Article