Abstract

I've been building Powerpoint-based quantum computers with electron spins in silicon for 20 years. Unfortunately, real-life-based quantum dot quantum computers are harder to implement. Materials, fabrication, and control challenges still impede progress. The way to accelerate discovery is to make and measure more qubits. Here I discuss separating the qubit realization and testing circuitry from the materials science and on-chip fabrication that will ultimately be necessary. This approach should allow us, in the shorter term, to characterize wafers non-invasively for their qubit-relevant properties, to make small qubit systems on various different materials with little extra cost, and even to test spin-qubit to superconducting cavity entanglement protocols where the best possible cavity quality is preserved. Such a testbed can advance the materials science of semiconductor quantum information devices and enable small quantum computers. This article may also be useful as a light and light-hearted introduction to quantum dot spin qubits.

Highlights

  • The two states of a qubit are realized in the spin of an electron, spin up and spin down

  • A spin qubit is formed from the Zeeman split sub-levels of the ground state of an electron trapped in some potential inside a semiconductor

  • When a positive bias is applied to the lead gates (L1 and L2) an accumulation layer of electrons is induced under the thin SiO2, to form the source and drain reservoirs for the double dot system

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Summary

Introduction

The two states of a qubit are realized in the spin of an electron, spin up and spin down. Temperature, noise, and gate operations can cause unwanted excitation into these states This so-called “valley splitting” problem, especially in silicon-germanium quantum dots, impacts yield, initialization/readout, and quantum operations, and originally motivated this work. Like for other qubit parameters such as coherence time and operation error rates, to measure the valley splitting one must fabricate a quantum dot and test it, typically at dilution refrigerator temperatures. Spin-based quantum dot qubits need multiple physical wires per dot and often nearby charge sensors (for spin-to-charge conversion-based readout [20]) This level of complexity in fabrication—which must be coupled with good materials science properties of the wafer and the gate stack—retards both new qubit exploration and characterizing many, individual quantum dots to optimize materials parameters. Cryogenic switches inside the DR will allow for a handful of quantum dot systems to be measured in sequence without a fridge warm-up

Making a quantum dot qubit without fabricating a quantum dot
12 Lateral quantum dot
RESULTS
Characterizing an induced quantum dot
Characterizing an induced quantum dot quantum computer
Caveat Emptor
What would I do?
One more thing: coupling spins to a superconducting cavity
End Speech
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