The simulated noise used to benchmark wavelet edge detection in this work was described incorrectly. The correct description is given here, and new results based on noise that matches the original description are provided. The results support our original conclusion, which is that wavelet edge detection outperforms thresholding in the presence of white noise and 1/fnoise.

The simulated noise used to benchmark wavelet edge detection in this work was described incorrectly. The correct description is given here, and new results based on noise that matches the original description are provided. The results support our original conclusion, which is that wavelet edge detection outperforms thresholding in the presence of white noise and 1/fnoise.

The operation of solid-state qubits often relies on single-shot readout using a nanoelectronic charge sensor, and the detection of events in a noisy sensor signal is crucial for high fidelity readout of such qubits. The most common detection scheme, comparing the signal to a threshold value, is accurate at low noise levels but is not robust to low-frequency noise and signal drift. We describe an alternative method for identifying charge sensor events using wavelet edge detection. The technique is convenient to use and we show that, with realistic signals and a single tunable parameter, wavelet detection can outperform thresholding and is significantly more tolerant to 1 / f ?> and low-frequency noise.

We investigate the tunnel rates and energies of excited states of small numbers of electrons in a quantum dot fabricated in a Si/SiGe heterostructure. Tunnel rates for loading and unloading electrons are found to be strongly energy dependent, and they vary significantly between different excited states. We show that this phenomenon enables charge sensing measurements of the average electron occupation that are analogous to Coulomb diamonds. Excited-state energies can be read directly from the plot, and we develop a rate model that enables a quantitative understanding of the relative sizes of different electron tunnel rates.

The holy grail of research in quantum computing is to simultaneously meet the DiVincenzo criteria—five obstacles that must be overcome to transform a quantum system into a scalable quantum computer [1]. Overcoming the first two, namely to have well-characterized qubits and long decoherence times can be a simple matter: Nature provides a variety of long-lived quantum systems. However, once the choice for a quantum system is made, things become quite complex since the other three criteria—qubit initialization, the implementation of quantum gates, and the qubit specific measurement capability (the so-called “quantum readout”)—require a number of different well-controlled interactions with individual qubits. Attempts to engineer these interactions have defined experimental quantum information research for the past two decades. Particularly challenging in this regard has been the measurement of a single qubit in a single attempt. Turning the isolation of qubits, needed for long coherence times, on and off in a controlled manner and determining the qubit state quickly with a single probe transition is crucial for the operation of quantum computers. (After all, “write-only memory” is not too useful.) Only when a qubit readout is available, will it be possible to experimentally verify initialization and quantum-gate operations.

We demonstrate single-shot readout of a silicon quantum dot spin qubit, and we measure the spin relaxation time T1. We show that the rate of spin loading can be tuned by an order of magnitude by changing the amplitude of a pulsed-gate voltage, and the fraction of spin-up electrons loaded can also be controlled. This tunability arises because electron spins can be loaded through an orbital excited state. Using a theory that includes excited states of the dot and energy-dependent tunneling, we find that a global fit to the loading rate and spin-up fraction is in good agreement with the data.

Quantum dots in Si have attracted recent interest due to the possibility of long spin relaxation and spin dephasing times in this material. Si/SiGe heterostructures are a particularly promising host for Si quantum dots, because the epitaxial interfaces that define the quantum well are believed to have very low defect density. Here we discuss recent results demonstrating that gate- tunable quantum dots containing individual electrons can be reproducibly produced in the Si/SiGe materials system. We discuss the tunability of the tunnel rates to the leads, the role of such tunnel rates in the determination of the absolute number of electrons in the quantum dots, and the role of the interdot tunnel rate in double quantum dots.

We report integrated charge sensing measurements on a Si/SIGe double quantum dot. The quantum dot Is shown to be tunable from a single, large dot to a well-isolated double dot. Charge sensing measurements enable the extraction of the tunnel coupling t between the quantum dots as a function of the voltage on the top gates defining the device. Control of the voltage on a single such gate tunes the barrier separating the two dots. The measured tunnel coupling is an exponential function of the gate voltage. The ability to control t is an Important step toward controlling spin qubits in silicon quantum dots.