Quantum non-demolition measurement of an electron spin qubit.

Measurements of quantum systems inevitably involve disturbance in various forms. Within the limits imposed by quantum mechanics, there exists an ideal projective measurement that does not introduce a back action on the measured observable, known as a quantum non-demolition (QND) measurement. Here we demonstrate an all-electrical QND measurement of a single electron spin in a gate-defined quantum dot.

A fast quantum interface between different spin qubit encodings.

Single-spin qubits in semiconductor quantum dots hold promise for universal quantum computation with demonstrations of a high single-qubit gate fidelity above 99.9% and two-qubit gates in conjunction with a long coherence time. However, initialization and readout of a qubit is orders of magnitude slower than control, which is detrimental for implementing measurement-based protocols such as error-correcting codes.

Coherent transfer of electron spin correlations assisted by dephasing noise.

Quantum coherence of superposed states, especially of entangled states, is indispensable for many quantum technologies. However, it is vulnerable to environmental noises, posing a fundamental challenge in solid-state systems including spin qubits. Here we show a scheme of entanglement engineering where pure dephasing assists the generation of quantum entanglement at distant sites in a chain of electron spins confined in semiconductor quantum dots.

Higher-order spin and charge dynamics in a quantum dot-lead hybrid system.

Understanding the dynamics of open quantum systems is important and challenging in basic physics and applications for quantum devices and quantum computing. Semiconductor quantum dots offer a good platform to explore the physics of open quantum systems because we can tune parameters including the coupling to the environment or leads. Here, we apply the fast single-shot measurement techniques from spin qubit experiments to explore the spin and charge dynamics due to tunnel coupling to a lead in a quantum dot-lead hybrid system.

Robust Single-Shot Spin Measurement with 99.5% Fidelity in a Quantum Dot Array.

We demonstrate a new method for projective single-shot measurement of two electron spin states (singlet versus triplet) in an array of gate-defined lateral quantum dots in GaAs. The measurement has very high fidelity and is robust with respect to electric and magnetic fluctuations in the environment. It exploits a long-lived metastable charge state, which increases both the contrast and the duration of the charge signal distinguishing the two measurement outcomes.