We study quantum coherence in a semiconductor charge qubit formed from a GaAs double quantum dot containing a single electron. Voltage pulses are applied to depletion gates to drive qubit rotations and noninvasive state readout is achieved using a quantum point contact charge detector. We measure a maximum coherence time of $\sim${}7\,\,ns at the charge degeneracy point, where the qubit level splitting is first-order insensitive to gate voltage fluctuations. We compare measurements of the coherence time as a function of detuning with numerical simulations and predictions from a 1/f noise model.

We introduce a solid-state qubit in which exchange interactions among confined electrons provide both the static longitudinal field and the oscillatory transverse field, allowing rapid and full qubit control via rf gate-voltage pulses. We demonstrate two-axis control at a detuning sweet spot, where leakage due to hyperfine coupling is suppressed by the large exchange gap. A $\pi /2$-gate time of 2.5 ns and a coherence time of $19\mu \mathrm{s}$, using multipulse echo, are also demonstrated. Model calculations that include effects of hyperfine noise are in excellent quantitative agreement with experiment.

Solid-state qubits have recently advanced to the level that enables them, in principle, to be scaled up into fault-tolerant quantum computers. As these physical qubits continue to advance, meeting the challenge of realizing a quantum machine will also require the development of new supporting devices and control architectures with complexity far beyond the systems used in today’s few-qubit experiments. Here, we report a microarchitecture for controlling and reading out qubits during the execution of a quantum algorithm such as an error-correcting code. We demonstrate the basic principles of this architecture using a cryogenic switch matrix implemented via high-electron-mobility transistors and a new kind of semiconductor device based on gate-switchable capacitance. The switch matrix is used to route microwave waveforms to qubits under the control of a field-programmable gate array, also operating at cryogenic temperatures. Taken together, these results suggest a viable approach for controlling large-scale quantum systems using semiconductor technology.

Splitting Quantum States: The ability to manipulate the spin and charge states in quantum dots electrically make them attractive as the building blocks (qubits) for quantum information processing systems. Petta et al. (p. 669 ; see the Perspective by Burkard ) now show that the avoided crossing of a spin-singlet state and spin-triplet state of a double quantum dot can operate as a state splitter. By controlling the rate at which an incoming state is swept across the crossing region, it can be separated into either the singlet or triplet states. The ability to manipulate the quantum states without needing high or local magnetic fields should prove useful in integrated quantum circuits.

We report the dispersive charge-state readout of a double quantum dot in the few-electron regime using the in situ gate electrodes as sensitive detectors. We benchmark this gate sensing technique against the well established quantum point contact charge detector and find comparable performance with a bandwidth of $$\sim${}10\text{ }\text{ }\mathrm{MHz}$ and an equivalent charge sensitivity of $$\sim${}6.3\ifmmode\times\else\texttimes\fi{}{10}^{-3}\text{ }\text{ }e/\sqrt{\mathrm{Hz}}$. Dispersive gate sensing alleviates the burden of separate charge detectors for quantum dot systems and promises to enable readout of qubits in scaled-up arrays.