22 research outputs found
Transport of Spin Qubits with Donor Chains under Realistic Experimental Conditions
The ability to transport quantum information across some distance can
facilitate the design and operation of a quantum processor. One-dimensional
spin chains provide a compact platform to realize scalable spin transport for a
solid-state quantum computer. Here, we model odd-sized donor chains in silicon
under a range of experimental non-idealities, including variability of donor
position within the chain. We show that the tolerance against donor placement
inaccuracies is greatly improved by operating the spin chain in a mode where
the electrons are confined at the Si-SiO interface. We then estimate the
required timescales and exchange couplings, and the level of noise that can be
tolerated to achieve high fidelity transport. We also propose a protocol to
calibrate and initialize the chain, thereby providing a complete guideline for
realizing a functional donor chain and utilizing it for spin transport.Comment: 19 pages, 12 figure
High-fidelity adiabatic inversion of a electron spin qubit in natural silicon
The main limitation to the high-fidelity quantum control of spins in
semiconductors is the presence of strongly fluctuating fields arising from the
nuclear spin bath of the host material. We demonstrate here a substantial
improvement in single-qubit gate fidelities for an electron spin qubit bound to
a P atom in natural silicon, by applying adiabatic inversion instead of
narrow-band pulses. We achieve an inversion fidelity of 97%, and we observe
signatures in the spin resonance spectra and the spin coherence time that are
consistent with the presence of an additional exchange-coupled donor. This work
highlights the effectiveness of adiabatic inversion techniques for spin control
in fluctuating environments.Comment: 4 pages, 2 figure
High mobility SiMOSFETs fabricated in a full 300mm CMOS process
The quality of the semiconductor–barrier interface plays a pivotal role in the demonstration of high quality reproducible quantum dots for quantum information processing. In this work, we have measured SiMOSFET Hall bars on undoped Si substrates in order to investigate the device quality. For devices fabricated in a full complementary metal oxide semiconductor (CMOS) process and of very thin oxide below a thickness of 10 nm, we report a record mobility of 17.5 × 103 cm2 V−1 s−1 indicating a high quality interface, suitable for future qubit applications. We also study the influence of gate materials on the mobilities and discuss the underlying mechanisms, giving insight into further material optimization for large scale quantum processors
Electrically controlling single spin qubits in a continuous microwave field
Large-scale quantum computers must be built upon quantum bits that are both
highly coherent and locally controllable. We demonstrate the quantum control of
the electron and the nuclear spin of a single 31P atom in silicon, using a
continuous microwave magnetic field together with nanoscale electrostatic
gates. The qubits are tuned into resonance with the microwave field by a local
change in electric field, which induces a Stark shift of the qubit energies.
This method, known as A-gate control, preserves the excellent coherence times
and gate fidelities of isolated spins, and can be extended to arbitrarily many
qubits without requiring multiple microwave sources.Comment: Main paper: 13 pages, 4 figures. Supplementary information: 25 pages,
13 figure
Modelling semiconductor spin qubits and their charge noise environment for quantum gate fidelity estimation
The spin of an electron confined in semiconductor quantum dots is currently a
promising candidate for quantum bit (qubit) implementations. Taking advantage
of existing CMOS integration technologies, such devices can offer a platform
for large scale quantum computation. However, a quantum mechanical framework
bridging a device's physical design and operational parameters to the qubit
energy space is lacking. Furthermore, the spin to charge coupling introduced by
intrinsic or induced Spin-Orbit-Interaction (SOI) exposes the qubits to charge
noise compromising their coherence properties and inducing quantum gate errors.
We present here a co-modelling framework for double quantum dot (DQD) devices
and their charge noise environment. We use a combination of an electrostatic
potential solver, full configuration interaction quantum mechanical methods and
two-level-fluctuator models to study the quantum gate performance in realistic
device designs and operation conditions. We utilize the developed models
together alongside the single electron solutions of the quantum dots to
simulate one- and two- qubit gates in the presence of charge noise. We find an
inverse correlation between quantum gate errors and quantum dot confinement
frequencies. We calculate X-gate fidelities >97% in the simulated Si-MOS
devices at a typical TLF densities. We also find that exchange driven two-qubit
SWAP gates show higher sensitivity to charge noise with fidelities down to 91%
in the presence of the same density of TLFs. We further investigate the one-
and two- qubit gate fidelities at different TLF densities. We find that given
the small size of the quantum dots, sensitivity of a quantum gate to the
distance between the noise sources and the quantum dot creates a strong
variability in the quantum gate fidelities which can compromise the device
yields in scaled qubit technologies.Comment: 23 pages , 16 figure