The protocols for controlled remote state preparation of a single qubit and a general two-qubit state are presented in this paper. The general pure three-qubit states are chosen as shared quantum channel, which are not Local operations and classical communication (LOCC) equivalent to the mostly used GHz state. This is the first time that general pure three-qubit states have been introduced to c...

Nielsen showed in quant-ph/0108020 that universal quantum computation can be performed using projective measurements, quantum memory, and preparation of the |0〉 state. Furthermore, 4-qubit measurements are sufficient. Fenner and Zhang showed in quant-ph/0111077 that 3-qubit measurements are sufficient. We prove that 2-qubit measurements are sufficient, closing the gap between the upper and lowe...

Within the lowest-order Born approximation, we calculate the exact dynamics of a qubit in the presence of 1/f noise, without Markov approximation. We show that the non-Markovian qubit timeevolution exhibits asymmetries and beatings that can be observed experimentally and cannot be explained within a Markovian theory. The present theory for 1/f noise is relevant for both spinand superconducting ...

We investigate coherent time evolution of charge states (pseudospin qubit) in a semiconductor double quantum dot. This fully tunable qubit is manipulated with a high-speed voltage pulse that controls the energy and decoherence of the system. Coherent oscillations of the qubit are observed for several combinations of many-body ground and excited states of the quantum dots. Possible decoherence m...

We present measurements of single-qubit gate errors for a superconducting qubit. Results from quantum process tomography and randomized benchmarking are compared with gate errors obtained from a double pi pulse experiment. Randomized benchmarking reveals a minimum average gate error of 1.1+/-0.3% and a simple exponential dependence of fidelity on the number of gates. It shows that the limits on...

We demonstrate feedback control of a superconducting transmon qubit using discrete, projective measurement and conditional coherent driving. Feedback realizes a fast and deterministic qubit reset to a target state with 2.4% error averaged over input superposition states, and allows concatenating experiments more than 10 times faster than by passive initialization. This closed-loop qubit control...

Stochastic local operations and classical communication (SLOCC), also called local filtering operations, are a convenient, useful set of quantum operations in grasping essential properties of entanglement. We give a quick overview about the characteristics of multipartite entanglement in terms of SLOCC, illustrating the 2-qubit and the rest (2 × 2 × n) quantum system. This not only includes cel...

The spectral decomposition is given for the N-qubit Bell operators with two observables per qubit. It is found that the eigenstates (when non-degenerate) are N-qubit GHZ states even for those operators that do not allow the maximal violation of the corresponding inequality. We present two applications of this analysis. In particular, we discuss the existence of pure entangled states that do not...

Title of dissertation: MULTI-JUNCTION EFFECTS IN DC SQUID PHASE QUBITS Benjamin K. Cooper, Doctor of Philosophy, 2013 Dissertation directed by: Professor Frederick C. Wellstood Department of Physics I discuss experimental and theoretical results on an LC filtered dc SQUID phase qubit. This qubit is an asymmetric aluminum dc SQUID, with junction critical currents 1.5 and 26.8 μA, on a sapphire s...

Since almost all quantum algorithms are represented in the quantum circuit model, the problem of finding a universal set of quantum gates is one the main problems in constructing quantum computers and implementing quantum algorithms. While it is rather easy to find a universal quantum basis, finding basis that satisfies some restrictions, due to implementation requirements, is far more challeng...