1,235 research outputs found
Optimized Compilation of Aggregated Instructions for Realistic Quantum Computers
Recent developments in engineering and algorithms have made real-world
applications in quantum computing possible in the near future. Existing quantum
programming languages and compilers use a quantum assembly language composed of
1- and 2-qubit (quantum bit) gates. Quantum compiler frameworks translate this
quantum assembly to electric signals (called control pulses) that implement the
specified computation on specific physical devices. However, there is a
mismatch between the operations defined by the 1- and 2-qubit logical ISA and
their underlying physical implementation, so the current practice of directly
translating logical instructions into control pulses results in inefficient,
high-latency programs. To address this inefficiency, we propose a universal
quantum compilation methodology that aggregates multiple logical operations
into larger units that manipulate up to 10 qubits at a time. Our methodology
then optimizes these aggregates by (1) finding commutative intermediate
operations that result in more efficient schedules and (2) creating custom
control pulses optimized for the aggregate (instead of individual 1- and
2-qubit operations). Compared to the standard gate-based compilation, the
proposed approach realizes a deeper vertical integration of high-level quantum
software and low-level, physical quantum hardware. We evaluate our approach on
important near-term quantum applications on simulations of superconducting
quantum architectures. Our proposed approach provides a mean speedup of
, with a maximum of . Because latency directly affects the
feasibility of quantum computation, our results not only improve performance
but also have the potential to enable quantum computation sooner than otherwise
possible.Comment: 13 pages, to apper in ASPLO
Towards understanding two-level-systems in amorphous solids -- Insights from quantum circuits
Amorphous solids show surprisingly universal behaviour at low temperatures.
The prevailing wisdom is that this can be explained by the existence of
two-state defects within the material. The so-called standard tunneling model
has become the established framework to explain these results, yet it still
leaves the central question essentially unanswered -- what are these two-level
defects? This question has recently taken on a new urgency with the rise of
superconducting circuits in quantum computing, circuit quantum electrodynamics,
magnetometry, electrometry and metrology. Superconducting circuits made from
aluminium or niobium are fundamentally limited by losses due to two-level
defects within the amorphous oxide layers encasing them. On the other hand,
these circuits also provide a novel and effective method for studying the very
defects which limit their operation. We can now go beyond ensemble measurements
and probe individual defects -- observing the quantum nature of their dynamics
and studying their formation, their behaviour as a function of applied field,
strain, temperature and other properties. This article reviews the plethora of
recent experimental results in this area and discusses the various theoretical
models which have been used to describe the observations. In doing so, it
summarises the current approaches to solving this fundamentally important
problem in solid-state physics.Comment: 34 pages, 7 figures, 1 tabl
Readout and Control Beyond a Few Qubits: Scaling-up Solid State Quantum Systems
Quantum entanglement and superposition, in addition to revealing interesting physics in their own right, can be harnessed as computational resources in a machine, enabling a range of algorithms for classically intractable problems. In recent years, experiments with small numbers of qubits have been demonstrated in a range of solid-state systems, but this is far from the numbers required to realise a useful quantum computer. In addition to the qubits themselves, quantum operation requires a host of classical electronics for control and readout, and current techniques used in few-qubit systems are not scalable. This thesis presents a series of techniques for control and readout of solid-state qubits, working towards scalability by integrating classical control with the quantum technology. Two techniques for reducing the footprint associated with readout of gallium arsenide spin qubits are demonstrated. Gate electrodes, used to define the quantum dot, are also shown to be sensitive state detectors. These gate-sensors, and the more conventional Quantum Point Contacts, are then multiplexed in the frequency domain, where three-channel qubit readout and ten-channel QPC readout are demonstrated. Two types of superconducting devices are also explored. The loss in superconducting coplanar waveguide resonators is measured, and a suppression of coupling to the parasitic electromagnetic environment is demonstrated. The thesis also details software for the simulation of Josephson-junction based circuits including features beyond what is available in commercial products. Finally, an architecture for managing control of a scalable machine is proposed where classical components are distributed throughout a cryostat and cryogenic switches route control pulses to the appropriate qubits. A simple implementation of the architecture is demonstrated that incorporates a double quantum dot, a gallium arsenide switch matrix, frequency multiplexed readout, and cryogenic classical computation
Characterizing Niobium Nitride Superconducting Microwave Coplanar Waveguide Resonator Array for Circuit Quantum Electrodynamics in Extreme Conditions
The high critical magnetic field and relatively high critical temperature of
niobium nitride (NbN) make it a promising material candidate for applications
in superconducting quantum technology. However, NbN-based devices and circuits
are sensitive to decoherence sources such as two-level system (TLS) defects.
Here, we numerically and experimentally investigate NbN superconducting
microwave coplanar waveguide resonator arrays, with a 100 nm thickness,
capacitively coupled to a common coplanar waveguide on a silicon chip. We
observe that the resonators' internal quality factor (Qi) decreases from Qi ~
1.07*10^6 in a high power regime ( = 27000) to Qi ~ 1.36 *10^5 in single
photon regime at temperature T = 100 mK. Data from this study is consistent
with the TLS theory, which describes the TLS interactions in resonator
substrates and interfaces. Moreover, we study the temperature dependence
internal quality factor and frequency tuning of the coplanar waveguide
resonators to characterise the quasiparticle density of NbN. We observe that
the increase in kinetic inductance at higher temperatures is the main reason
for the frequency shift. Finally, we measure the resonators' resonance
frequency and internal quality factor at single photon regime in response to
in-plane magnetic fields B||. We verify that Qi stays well above 10^4 up to B||
= 240 mT in the photon number = 1.8 at T = 100 mK. Our results may pave
the way for realising robust microwave superconducting circuits for circuit
quantum electrodynamics (cQED) at high magnetic fields necessary for
fault-tolerant quantum computing, and ultrasensitive quantum sensing
Fault-Tolerant Computing With Biased-Noise Superconducting Qubits
We present a universal scheme of pulsed operations for the IBM
oscillator-stabilized flux qubit comprising the CPHASE gate, single-qubit
preparations and measurements. Based on numerical simulations, we argue that
the error rates for these operations can be as low as about .5% and that noise
is highly biased, with phase errors being stronger than all other types of
errors by a factor of nearly 10^3. In contrast, the design of a CNOT gate for
this system with an error rate of less than about 1.2% seems extremely
challenging. We propose a special encoding which exploits the noise bias
allowing us to implement a logical CNOT gate where phase errors and all other
types of errors have nearly balanced rates of about .4%. Our results illustrate
how the design of an encoding scheme can be adjusted and optimized according to
the available physical operations and the particular noise characteristics of
experimental devices.Comment: 15 pages, 7 figure
Roadmap on quantum optical systems
This roadmap bundles fast developing topics in experimental optical quantum sciences, addressing current challenges as well as potential advances in future research. We have focused on three main areas: quantum assisted high precision measurements, quantum information/simulation, and quantum gases. Quantum assisted high precision measurements are discussed in the first three sections, which review optical clocks, atom interferometry, and optical magnetometry. These fields are already successfully utilized in various applied areas. We will discuss approaches to extend this impact even further. In the quantum information/simulation section, we start with the traditionally successful employed systems based on neutral atoms and ions. In addition the marvelous demonstrations of systems suitable for quantum information is not progressing, unsolved challenges remain and will be discussed. We will also review, as an alternative approach, the utilization of hybrid quantum systems based on superconducting quantum devices and ultracold atoms. Novel developments in atomtronics promise unique access in exploring solid-state systems with ultracold gases and are investigated in depth. The sections discussing the continuously fast- developing quantum gases include a review on dipolar heteronuclear diatomic gases, Rydberg gases, and ultracold plasma. Overall, we have accomplished a roadmap of selected areas undergoing rapid progress in quantum optics, highlighting current advances and future challenges. These exciting developments and vast advances will shape the field of quantum optics in the future
JETC (Japanese Technology Evaluation Center) Panel Report on High Temperature Superconductivity in Japan
The Japanese regard success in R and D in high temperature superconductivity as an important national objective. The results of a detailed evaluation of the current state of Japanese high temperature superconductivity development are provided. The analysis was performed by a panel of technical experts drawn from U.S. industry and academia, and is based on reviews of the relevant literature and visits to Japanese government, academic and industrial laboratories. Detailed appraisals are presented on the following: Basic research; superconducting materials; large scale applications; processing of superconducting materials; superconducting electronics and thin films. In all cases, comparisons are made with the corresponding state-of-the-art in the United States
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