Photon- and phonon-assisted tunneling in the three-dimensional charge stability diagram of a triple quantum dot array

We report both photon- and phonon-assisted tunneling transitions in a linear array of three quantum dots, which can only be understood by considering the full three-dimensionality of the charge stability diagram. Such tunneling transitions potentially contribute to leakage of qubits defined in this system. A detailed understanding of these...

Silicon Quantum Electronics

Low-crosstalk bifurcation detectors for coupled flux qubits

We present experimental results on the crosstalk between two ac-operated dispersive bifurcation detectors, implemented in a circuit for high-fidelity readout of two strongly coupled flux qubits. Both phase-dependent and phase-independent contributions to the crosstalk are analyzed. For proper tuning of the phase the measured crosstalk is 0.1%...

Coherent transport through a double donor system in silicon

In this letter, we describe the observation of the interference of conduction paths induced by two donors in a nanoscale silicon transistor, resulting in a Fano resonance. This demonstrates the coherent exchange of electrons between two donors. In addition, the phase difference between the two conduction paths can be tuned by means of a magnetic...

Electrical manipulation and detection of single electron spins in quantum dots

Entanglement in Solid-State Nanostructures

The goal of this thesis is to investigate theoretically the generation and behaviour of multipartite entanglement for solid-state nanosystems, in particular electron spin quantum bits (so-called 'qubits') in quantum dots. A quantum dot is a tiny potential well where a single electron can be trapped. A quantum bit can be implemented in this...

Multiparticle entanglement under the influence of decoherence

We present a method to determine the decay of multiparticle quantum correlations as quantified by the geometric measure of entanglement under the influence of decoherence. With this, we compare the robustness of entanglement in Greenberger-Horne-Zeilinger (GHZ), cluster, W, and Dicke states of four qubits and show that the Dicke state is the...

Manipulation and Read-out of Spins in Quantum Dots

Besides an electric charge, electrons also have a tiny magnetic moment, called spin. In a magnetic field, the spin has two possible orientations: 'spin-up' (parallel to the field) and 'spin-down' (anti-parallel to the field) and can therefore be used as a quantum bit, the computational unit of a quantum computer. For quantum computations,...

Role of relaxation in the quantum measurement of a superconducting qubit using a nonlinear oscillator

We analyze the relaxation of a superconducting flux qubit during measurement. The qubit state is measured with a nonlinear oscillator driven across the threshold of bifurcation, acting as a switching dispersive detector. This readout scheme is of quantum nondemolition type. Two successive readouts are used to analyze the evolution of the qubit...

Statistics of measurement of noncommuting quantum variables: Monitoring and purification of a qubit

We address continuous weak linear quantum measurement and argue that it is best understood in terms of statistics of the outcomes of the linear detectors measuring a quantum system, for example, a qubit. We mostly concentrate on a setup consisting of a qubit and three independent detectors that simultaneously monitor three noncommuting operator...

Interqubit coupling mediated by a high-excitation-energy quantum object

We consider a system composed of two qubits and a high excitation energy quantum object used to mediate coupling between the qubits. We treat the entire system quantum mechanically and analyze the properties of the eigenvalues and eigenstates of the total Hamiltonian. After reproducing well known results concerning the leading term in the...

Low-frequency noise in Josephson junctions for superconducting qubits

The authors have studied low-frequency resistance fluctuations in shadow-evaporated Al/AlOx/Al tunnel junctions. Between 300 and 5?K the spectral density follows a 1/f law. Below 5?K, individual defects distort the 1/f shape of the spectrum. The spectral density decreases linearly with temperature between 150 and 1?K and saturates below 0.8?K....

Fault-tolerant architectures for nanoelectronic and quantum devices

The progress in CMOS technology has entered the sub-micron realm, and the technology will approach its limits within about 15 years. Already various novel information processing devices, based on quantum mechanical effects at the nanometer scale, have been widely investigated and some have been successfully demonstrated at the circuit level....