Pasquale Scarlino

Electrical control of a long-lived spin qubit in a Si/SiGe quantum dot

Nanofabricated quantum bits permit large-scale integration but usually suffer from short coherence times due to interactions with their solid-state environment. The outstanding challenge is to engineer the environment so that it minimally affects the qubit, but still allows qubit control and scalability. Here, we demonstrate a long-lived single-electron spin qubit in a Si/SiGe quantum dot with all-electrical two-axis control. The spin is driven by resonant microwave electric fields in a transverse magnetic field gradient from a local micromagnet, and the spin state is read out in the single-shot mode. Electron spin resonance occurs at two closely spaced frequencies, which we attribute to two valley states. Thanks to the weak hyperfine coupling in silicon, a Ramsey decay timescale of 1 μs is observed, almost two orders of magnitude longer than the intrinsic timescales in GaAs quantum dots, whereas gate operation times are comparable to those reported in GaAs. The spin echo decay time is ~40 μs, both with one and four echo pulses, possibly limited by intervalley scattering. These advances strongly improve the prospects for quantum information processing based on quantum dots.

High-Kinetic-Inductance Superconducting Nanowire Resonators for Circuit QED in a Magnetic Field

We present superconducting microwave-frequency resonators based on NbTiN nanowires. The small cross section of the nanowires minimizes vortex generation, making the resonators resilient to magnetic fields. Measured intrinsic quality factors exceed

Strong Coupling Cavity QED with Gate-Defined Double Quantum Dots Enabled by a High Impedance Resonator

2\times 10^5

Gate fidelity and coherence of an electron spin in an Si/SiGe quantum dot with micromagnet

in a

Second-Harmonic Coherent Driving of a Spin Qubit in a Si/SiGe Quantum Dot.

6

Dressed photon-orbital states in a quantum dot: Intervalley spin resonance

T in-plane magnetic field, and

Coherent spin-photon coupling using a resonant exchange qubit

3\times 10^4

Excitation of a Si/SiGe quantum dot using an on-chip microwave antenna

in a

Valley dependent anisotropic spin splitting in silicon quantum dots

350

Spin-Relaxation Anisotropy in a GaAs Quantum Dot

mT perpendicular magnetic field. Due to their high characteristic impedance, these resonators are expected to develop zero-point voltage fluctuations one order of magnitude larger than in standard coplanar waveguide resonators. These properties make the nanowire resonators well suited for circuit QED experiments needing strong coupling to quantum systems with small electric dipole moments and requiring a magnetic field, such as electrons in single and double quantum dots.