Preliminary Report on the Seismological and Engineering Aspects of the January 17, 1994 Northridge Earthquake

This report on the seismological and engineering aspects of the 17 January, 1994, Northridge earthquake was printed on 24 January, 1994, one week after the main event. Its purpose is to provide a brief overview of preliminary observations related to the earthquake. The primary audience is seismologists, engineers and related professionals in the earthquake hazard and earthquake risk mitigation field. The report is preliminary in the sense that significant data collection and analysis remain to be completed. Reports containing more complete data and analysis may be issued at a later date. Immediately following the 17 January, 1994, Northridge earthquake, the Earthquake Engineering Research Center dispatched a reconnaissance team to the epicentral region. This report, issued one week after the earthquake, provides an overview of the seismological and engineering aspects of the earthquake and associated aftershocks. A slide set containing approximately 1 00 slides obtained during the reconnaissance, including all slides and photographs in this report, is being prepared. Copies of the set are available at cost. To obtain a set, write to EERC Reports, 1301 S. 46th Street, Richmond, California 94804, e-mail to [email protected], call510-231-9468, or fax 510-231-9461.National Science Foundation///Virginia, Estados UnidosUCR::Vicerrectoría de Docencia::Ingeniería::Facultad de Ingeniería::Escuela de Ingeniería Civi

Bounds to electron spin qubit variability for scalable CMOS architectures

Spins of electrons in CMOS quantum dots combine exquisite quantum properties and scalable fabrication. In the age of quantum technology, however, the metrics that crowned Si/SiO2 as the microelectronics standard need to be reassessed with respect to their impact upon qubit performance. We chart the spin qubit variability due to the unavoidable atomic-scale roughness of the Si/SiO$_2$ interface, compiling experiments in 12 devices, and developing theoretical tools to analyse these results. Atomistic tight binding and path integral Monte Carlo methods are adapted for describing fluctuations in devices with millions of atoms by directly analysing their wavefunctions and electron paths instead of their energy spectra. We correlate the effect of roughness with the variability in qubit position, deformation, valley splitting, valley phase, spin-orbit coupling and exchange coupling. These variabilities are found to be bounded and lie within the tolerances for scalable architectures for quantum computing as long as robust control methods are incorporated.Comment: 20 pages, 8 figure

Impact of electrostatic crosstalk on spin qubits in dense CMOS quantum dot arrays

Quantum processors based on integrated nanoscale silicon spin qubits are a promising platform for highly scalable quantum computation. Current CMOS spin qubit processors consist of dense gate arrays to define the quantum dots, making them susceptible to crosstalk from capacitive coupling between a dot and its neighbouring gates. Small but sizeable spin-orbit interactions can transfer this electrostatic crosstalk to the spin g-factors, creating a dependence of the Larmor frequency on the electric field created by gate electrodes positioned even tens of nanometers apart. By studying the Stark shift from tens of spin qubits measured in nine different CMOS devices, we developed a theoretical frawework that explains how electric fields couple to the spin of the electrons in increasingly complex arrays, including those electric fluctuations that limit qubit dephasing times $T_2^*$. The results will aid in the design of robust strategies to scale CMOS quantum technology.Comment: 9 pages, 4 figure

High-fidelity operation and algorithmic initialisation of spin qubits above one kelvin

The encoding of qubits in semiconductor spin carriers has been recognised as a promising approach to a commercial quantum computer that can be lithographically produced and integrated at scale. However, the operation of the large number of qubits required for advantageous quantum applications will produce a thermal load exceeding the available cooling power of cryostats at millikelvin temperatures. As the scale-up accelerates, it becomes imperative to establish fault-tolerant operation above 1 kelvin, where the cooling power is orders of magnitude higher. Here, we tune up and operate spin qubits in silicon above 1 kelvin, with fidelities in the range required for fault-tolerant operation at such temperatures. We design an algorithmic initialisation protocol to prepare a pure two-qubit state even when the thermal energy is substantially above the qubit energies, and incorporate high-fidelity radio-frequency readout to achieve an initialisation fidelity of 99.34 per cent. Importantly, we demonstrate a single-qubit Clifford gate fidelity of 99.85 per cent, and a two-qubit gate fidelity of 98.92 per cent. These advances overcome the fundamental limitation that the thermal energy must be well below the qubit energies for high-fidelity operation to be possible, surmounting a major obstacle in the pathway to scalable and fault-tolerant quantum computation

Consistency of high-fidelity two-qubit operations in silicon

The consistency of entangling operations between qubits is essential for the performance of multi-qubit systems, and is a crucial factor in achieving fault-tolerant quantum processors. Solid-state platforms are particularly exposed to inconsistency due to the materials-induced variability of performance between qubits and the instability of gate fidelities over time. Here we quantify this consistency for spin qubits, tying it to its physical origins, while demonstrating sustained and repeatable operation of two-qubit gates with fidelities above 99% in the technologically important silicon metal-oxide-semiconductor (SiMOS) quantum dot platform. We undertake a detailed study of the stability of these operations by analysing errors and fidelities in multiple devices through numerous trials and extended periods of operation. Adopting three different characterisation methods, we measure entangling gate fidelities ranging from 96.8% to 99.8%. Our analysis tools also identify physical causes of qubit degradation and offer ways to maintain performance within tolerance. Furthermore, we investigate the impact of qubit design, feedback systems, and robust gates on implementing scalable, high-fidelity control strategies. These results highlight both the capabilities and challenges for the scaling up of spin-based qubits into full-scale quantum processors