Theory of control and quantum state measurement with squeezed microwaves in superconducting circuits

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Precise, large scale control of qubit(s) dynamics is a major challenge today for quantum information processing (QIP) in all competing architectures. We propose to utilise squeezed microwave sources and achieve new ways of controlling and measuring qubits in closed networks with superconducting qubit-cavity nodes connected by transmission lines, when exclusively coupled to these squeezed fields. Existing experimental methods employ coherent (classical) microwave fields. Strong and high-quality sources of non-classical squeezed microwave radiation have become widely available at laboratories that specialise in implementations of superconducting qubits. Our hypothesis is that driven qubit(s) dynamics will be also inherently different and that would open new possibilities of control and measurement. Our collaboration recently succeeded in efficiently coupling a qubit exclusively to the microwave electromagnetic modes of a frequency broadband squeezed vacuum. The influence of this radiation on the dissipative qubit dynamics was then demonstrated for the first time. A natural step forward is to investigate theoretically the potential of this breakthrough for applications in QIP. Building on the feasibility of exclusive reservoirs we now wish to: (1) theoretically analyse the propagation/transmission of squeezed states in the network and the resulting driven superconducting qubit-cavity dynamics, and based on this (2) develop methods of high fidelity quantum state control and measurement for single and multi-qubit devices. Methods of increased fidelity would have direct impact on scaling-up the control of larger qubit networks and to the realisation of efficient quantum error detection and correction.