Development of a Josephson Parametric Amplifier for the Preparation and Detection of Nonclassical States of Microwave Fields

<p>Recent innovations in the technology of superconducting circuits have made it possible to create nonclassical states of microwave light fields. These states are usually associated with the subject of quantum optics. The ability to manipulate quantum states of microwave light fields holds out the promise of building dense integrable cir- cuits to process quantum information electrically. However, a major difficulty lies in the fact that there is no general purpose method of efficiently measuring the quantum state of a microwave field. In this thesis, I describe the development of an amplifier, based on a Josephson parametric amplifier. This new parametric amplifier enables this kind of efficient measurement. Although parametric amplifiers are narrowband (only ampli- fying signals in a narrow frequency range around a central frequency), I have developed an amplifier whose central frequency is widely tunable (a full octave, 4\textendash8 GHz), greatly improving its usefulness. I have studied the gain, bandwidth, dynamic range, and added noise of the amplifier. I have shown that when operated in a particular manner, known as degenerate mode, the parametric amplifier adds less noise than the noise associated with the quantum fluctuations of the electromagnetic vacuum. In addition, its gain is large enough to ensure that the amplified vacuum noise overwhelms the noise added by conventional amplifiers that follow the parametric amplifier. Together, these two fea- tures make it possible to measure either the phase or amplitude of a microwave signal where the dominant uncertainty comes from the quantum noise of the signal itself. In addition, a degenerate parametric amplifier also prepares particular nonclassical states called squeezed states. Our parametric amplifier prepares squeezed states, which have (in one of its quadratures) noise with a variance less than one tenth that of the vacuum noise. I have employed the parametric amplifier in two experiments that require its abil- ity to make efficient measurements. First, I used the parametric amplifier to determine the full density matrix of a squeezed state generated by a second parametric amplifier. Second, I used the amplifier to enable a measurement of position with precision bet- ter than the value at the standard quantum limit. These demonstrations are powerful evidence that we have indeed realized a general-purpose quantum-efficient method of measuring microwave fields.</p>
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University of Colorado Boulder
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