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**Harvard**

Tornberg, L. (2009) *Superconducting qubits - measurement, entanglement, and noise*. Göteborg : Chalmers University of Technology (Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie, nr: 2960).

** BibTeX **

@book{

Tornberg2009,

author={Tornberg, Lars},

title={Superconducting qubits - measurement, entanglement, and noise},

isbn={978-91-7385-279-1 },

abstract={In the early 1980’s, it was suggested that a computer obeying the laws of
quantum mechanics would be able to solve problems beyond the capabilities
of a classical computer. The novel ways in which such a quantum computer
works relies on the quantum properties of the quantum bits (qubits) used to
store the information. Any candidate for a quantum computer must thus be
able to sustain these properties and offer means to manipulate and read-out
the information. One such candidate are quantum mechanical, superconducting circuits, where the logical bit is encoded in the energy eigenstates of
the system. In circuit quantum electrodynamics, such a qubit is coupled to a
microwave cavity allowing the qubit to be coherently controlled and read-out
by probing the cavity. In this thesis, we theoretically investigate the destructive effects of noise which couple to the system as one tries to measure and
control the qubits. We study the so called quantum capacitance read-out
scheme, where the state of the qubit is mapped onto an equivalent capacitance of the circuit. It is shown that this is quantum limited, in the sense
that the state of the qubit can be determined while simultaneously adding
a minimum amount of noise to the system. Apart from the added noise,
a measurement on a qubit will perturb it, causing the state to collapse to
one of the measurement eigenstates. Such a state collapse can be utilized to
generate entanglement between qubits by measuring on the cavity. We show
that high-fidelity entangled states can be produced in this way and discuss
the potential of the measurement to violate a bound given by local hidden
variable theories. The possibility to prolong the life-time of the quantum
state by active error correction is also investigated and we discuss limits on
gate operation times to benefit from such a code, given realistic values for
the error probabilities.
This work was supported by the European Commission through IST-015708
EuroSQIP integrated pro ject, and by the Swedish Research Council. },

publisher={Institutionen för mikroteknologi och nanovetenskap, Tillämpad kvantfysik, Chalmers tekniska högskola,},

place={Göteborg},

year={2009},

series={Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie, no: 2960Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology, no: 143},

keywords={Quantum Computing, Superconducting Qubits, Quantum Electric Circuits, Quantum Measurement, Open Quantum Systems, Quantum Optics},

note={89},

}

** RefWorks **

RT Dissertation/Thesis

SR Print

ID 93315

A1 Tornberg, Lars

T1 Superconducting qubits - measurement, entanglement, and noise

YR 2009

SN 978-91-7385-279-1

AB In the early 1980’s, it was suggested that a computer obeying the laws of
quantum mechanics would be able to solve problems beyond the capabilities
of a classical computer. The novel ways in which such a quantum computer
works relies on the quantum properties of the quantum bits (qubits) used to
store the information. Any candidate for a quantum computer must thus be
able to sustain these properties and offer means to manipulate and read-out
the information. One such candidate are quantum mechanical, superconducting circuits, where the logical bit is encoded in the energy eigenstates of
the system. In circuit quantum electrodynamics, such a qubit is coupled to a
microwave cavity allowing the qubit to be coherently controlled and read-out
by probing the cavity. In this thesis, we theoretically investigate the destructive effects of noise which couple to the system as one tries to measure and
control the qubits. We study the so called quantum capacitance read-out
scheme, where the state of the qubit is mapped onto an equivalent capacitance of the circuit. It is shown that this is quantum limited, in the sense
that the state of the qubit can be determined while simultaneously adding
a minimum amount of noise to the system. Apart from the added noise,
a measurement on a qubit will perturb it, causing the state to collapse to
one of the measurement eigenstates. Such a state collapse can be utilized to
generate entanglement between qubits by measuring on the cavity. We show
that high-fidelity entangled states can be produced in this way and discuss
the potential of the measurement to violate a bound given by local hidden
variable theories. The possibility to prolong the life-time of the quantum
state by active error correction is also investigated and we discuss limits on
gate operation times to benefit from such a code, given realistic values for
the error probabilities.
This work was supported by the European Commission through IST-015708
EuroSQIP integrated pro ject, and by the Swedish Research Council.

PB Institutionen för mikroteknologi och nanovetenskap, Tillämpad kvantfysik, Chalmers tekniska högskola,

T3 Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie, no: 2960Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology, no: 143

LA eng

OL 30