WARF: P04175US
Spin Readout and Initialization in Semiconductor Quantum Dots

INVENTORS

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Mark Friesen, Mark Eriksson, Charles Tahan, Robert Joynt

Quantum computers use quantum particles (e.g., electrons), called qubits, to process information, instead of bits as in classical, serial computing. Unlike bits, which exist in either the 0 or 1 state, qubits can exist in more than one state at once – a characteristic that allows quantum computers to calculate all the possible solutions to a problem simultaneously instead of one-by-one like their less powerful, serial counterparts.

Previously, a team of UW-Madison scientists designed a scalable, multilayer semiconductor architecture that provides a framework for trapping individual electrons (qubits) in a solid and bringing them close to each other. The architecture also allows manipulation of the electrons’ individual spin states, while maintaining their coherence (see link below). UW-Madison researchers have now developed a semiconductor-based, quantum dot scheme for enabling measurement of the spin states of individual qubits without the need for additional external couplings that can cause decoherence. In this quantum dot scheme, the energy levels of trapped qubits are controlled by varying the voltages of nearby metal gates. By bringing specific energy levels into resonance with an applied microwave field, the qubits can be made to undergo spin-dependent oscillations that are detected by a single electron transistor.

• Quantum computing

• Measures the spin states of qubits without the need for additional external couplings, as proposed in other readout schemes
• Allows spin readout while keeping qubits isolated, thus minimizing environmental decoherence
• Can also be used to rapidly initialize a qubit to its final state, an important requirement for quantum computing
• Initialization by this method (as opposed to initialization by thermalization) eliminates the need for spin-polarized leads or ancillary qubits
• Device may be incorporated into various materials systems, including GaAs/AlGaAs and Si/SiGe heterostructures.

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