Quantum Class 15, Thurs 2020-17-22
Table of contents
1 Quantum hardware
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The transmon qubit | QuTech Academy 6:03.
The Hamiltonian of a system is an equation for its total energy (kinetic and potential) in terms of parameters like position and momentum.
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Alexandre Blais - Quantum Computing with Superconducting Qubits (Part 1) - CSSQI 2012 45:11.
We'll watch part. You're encouraged to finish it on your own.
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Control of transmon qubits using a cryogenic CMOS integrated circuit (QuantumCasts) 35:47.
Control of transmon qubits using a cryogenic CMOS integrated circuit talk is presented by Research Scientist Joe Bardin for the APS March Meeting 2020.
Superconducting quantum processors are controlled and measured in the analog domain and the design of the associated classical-to-quantum interface is critical in optimizing the overall performance of the quantum computer. Control of the processor is achieved using a combination of carefully shaped microwave pulses and high-precision time varying flux biases. Measurement of quantum states is typically achieved using dispersive readout, which requires a low-power pulsed microwave drive and a near quantum-limited readout chain. For control of a single qubit, a typical system employs two high-speed high-resolution (e.g., 1 Gsps/14 bit) digital-to-analog converters (DACs) and a single-sideband modulator to generate microwave control pulses. A third DAC with similar specifications is used for flux-bias control. A typical readout channel may service on the order of five qubits and contains yet another pair of DACs, with a single-sideband modulator employed to generate a stimulus signal. For measurement, the readout chain also employs a series of cryogenic amplifiers followed by further amplification, IQ demodulation, and high-speed digitization at room temperature. For today’s prototype systems with on the order of 50-100 qubits, keeping most of the electronics at room temperature makes sense. However, achieving fault tolerance—a long term goal of the community—will require implementing systems with on the order of 10^6 qubits and today’s brute force control and readout approach will not scale to these levels. Instead, a more integrated approach will be required. In this talk, we will present a review of recent work towards implementing a scalable cryogenic quantum control and readout system using silicon integrated circuit technology. After motivating the work, we will describe the design and characterization of a prototype cryogenic XY controller for transmon qubits. Detailed measurement results will be presented. The talk will conclude with a discussion of future work.
You may watch this on your own.
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Per Delsing: Superconducting qubits as artificial atoms 28:59.
I might start showing this around 6:00 and show to around 16:00. He's describing a different computer from IBM's.
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The Taming of the Superconducting Qubit: A Tale of Loss 35:47.
Presenter: Conal Murray, Research Staff Member, IBM Research
The potential of quantum computing to enable new ways of solving problems considered intractable on classical computing platforms relies on our understanding of how qubits operate. Qubit scaling follows different metrics than those associated with classical computing, driven by the requirement that the fragile states they possess can be retained for sufficiently long times. After a brief introduction into superconducting transmon qubits, I will discuss how dielectric loss impacts their relaxation times and how we can effectively model such behavior using analytical and computational approaches. The resulting analysis provides guidance into the design aspects associated with such qubits. A secondary issue that follows from manufacturing greater numbers of qubits involves unwanted communication among them. In particular, resonance modes generated in the substrate on which they reside can limit their operating frequencies. It is known that incorporating grounded, through-silicon vias can increase the corresponding cutoff frequency within the substrate. I will show how we can predict the resulting spectrum by considering the array of vias as an effective photonic crystal to arrive at a fundamental frequency dependent on the particulars of the via geometry.
http://meetings.aps.org/Meeting/MAR20/Session/P28.2
We may watch the first part. This talk is more technical.
2 QuTech Academy
We've seen some of the excellent videos from this Delft research group.