274 research outputs found
Thermionic charge transport in CMOS nano-transistors
We report on DC and microwave electrical transport measurements in
silicon-on-insulator CMOS nano-transistors at low and room temperature. At low
source-drain voltage, the DC current and RF response show signs of conductance
quantization. We attribute this to Coulomb blockade resulting from barriers
formed at the spacer-gate interfaces. We show that at high bias transport
occurs thermionically over the highest barrier: Transconductance traces
obtained from microwave scattering-parameter measurements at liquid helium and
room temperature is accurately fitted by a thermionic model. From the fits we
deduce the ratio of gate capacitance and quantum capacitance, as well as the
electron temperature
Charge dynamics and spin blockade in a hybrid double quantum dot in silicon
Electron spin qubits in silicon, whether in quantum dots or in donor atoms,
have long been considered attractive qubits for the implementation of a quantum
computer due to the semiconductor vacuum character of silicon and its
compatibility with the microelectronics industry. While donor electron spins in
silicon provide extremely long coherence times and access to the nuclear spin
via the hyperfine interaction, quantum dots have the complementary advantages
of fast electrical operations, tunability and scalability. Here we present an
approach to a novel hybrid double quantum dot by coupling a donor to a
lithographically patterned artificial atom. Using gate-based rf reflectometry,
we probe the charge stability of this double quantum dot system and the
variation of quantum capacitance at the interdot charge transition. Using
microwave spectroscopy, we find a tunnel coupling of 2.7 GHz and characterise
the charge dynamics, which reveals a charge T2* of 200 ps and a relaxation time
T1 of 100 ns. Additionally, we demonstrate spin blockade at the inderdot
transition, opening up the possibility to operate this coupled system as a
singlet-triplet qubit or to transfer a coherent spin state between the quantum
dot and the donor electron and nucleus.Comment: 6 pages, 4 figures, supplementary information (3 pages, 4 figures
Scaling silicon-based quantum computing using CMOS technology: State-of-the-art, Challenges and Perspectives
Complementary metal-oxide semiconductor (CMOS) technology has radically
reshaped the world by taking humanity to the digital age. Cramming more
transistors into the same physical space has enabled an exponential increase in
computational performance, a strategy that has been recently hampered by the
increasing complexity and cost of miniaturization. To continue achieving
significant gains in computing performance, new computing paradigms, such as
quantum computing, must be developed. However, finding the optimal physical
system to process quantum information, and scale it up to the large number of
qubits necessary to build a general-purpose quantum computer, remains a
significant challenge. Recent breakthroughs in nanodevice engineering have
shown that qubits can now be manufactured in a similar fashion to silicon
field-effect transistors, opening an opportunity to leverage the know-how of
the CMOS industry to address the scaling challenge. In this article, we focus
on the analysis of the scaling prospects of quantum computing systems based on
CMOS technology.Comment: Comments welcom
Pipeline quantum processor architecture for silicon spin qubits
Noisy intermediate-scale quantum (NISQ) devices seek to achieve quantum
advantage over classical systems without the use of full quantum error
correction. We propose a NISQ processor architecture using a qubit `pipeline'
in which all run-time control is applied globally, reducing the required number
and complexity of control and interconnect resources. This is achieved by
progressing qubit states through a layered physical array of structures which
realise single and two-qubit gates. Such an approach lends itself to NISQ
applications such as variational quantum eigensolvers which require numerous
repetitions of the same calculation, or small variations thereof. In exchange
for simplifying run-time control, a larger number of physical structures is
required for shuttling the qubits as the circuit depth now corresponds to an
array of physical structures. However, qubit states can be `pipelined' densely
through the arrays for repeated runs to make more efficient use of physical
resources. We describe how the qubit pipeline can be implemented in a silicon
spin-qubit platform, to which it is well suited to due to the high qubit
density and scalability. In this implementation, we describe the physical
realisation of single and two qubit gates which represent a universal gate set
that can achieve fidelities of , even under typical
qubit frequency variations.Comment: 21 pages (13 for main + 8 for supplement), 9 figures (4 for main + 5
for supplement
Alternative fast quantum logic gates using nonadiabatic Landau-Zener-St\"{u}ckelberg-Majorana transitions
A conventional realization of quantum logic gates and control is based on
resonant Rabi oscillations of the occupation probability of the system. This
approach has certain limitations and complications, like counter-rotating
terms. We study an alternative paradigm for implementing quantum logic gates
based on Landau-Zener-St\"{u}ckelberg-Majorana (LZSM) interferometry with
non-resonant driving and the alternation of adiabatic evolution and
non-adiabatic transitions. Compared to Rabi oscillations, the main differences
are a non-resonant driving frequency and a small number of periods in the
external driving. We explore the dynamics of a multilevel quantum system under
LZSM drives and optimize the parameters for increasing single- and two-qubit
gates speed. We define the parameters of the external driving required for
implementing some specific gates using the adiabatic-impulse model. The LZSM
approach can be applied to a large variety of multi-level quantum systems and
external driving, providing a method for implementing quantum logic gates on
them.Comment: 15 pages, 12 figure
Gate-based spin readout of hole quantum dots with site-dependent factors
The rapid progress of hole spin qubits in group IV semiconductors has been
driven by their potential for scalability. This is owed to the compatibility
with industrial manufacturing standards, as well as the ease of operation and
addressability via all-electric drives. However, owing to a strong spin-orbit
interaction, these systems present variability and anisotropy in key qubit
control parameters such as the Land\'e factor, requiring careful
characterisation for reliable qubit operation. Here, we experimentally
investigate a hole double quantum dot in silicon by carrying out spin readout
with gate-based reflectometry. We show that characteristic features in the
reflected phase signal arising from magneto-spectroscopy convey information on
site-dependent factors in the two dots. Using analytical modeling, we
extract the physical parameters of our system and, through numerical
calculations, we extend the results to point out the prospect of conveniently
extracting information about the local factors from reflectometry
measurements.Comment: Main manuscript: 12 pages, 8 figures. Supplementary Information: 3
pages, 2 figure
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