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

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.

Academia

Superconducting circuits are becoming an ever more successful platform to develop ideas in quantum optics as we have also shown in our recent experiment. Building on that we plan to use well developed theoretical methods to impact techniques of control and measurement of quantum information. Therefore the academic impact we believe will be in both areas: a revival of ideas related to squeezed states, and in turn, expanding the set of tools for coherent control. The timeliness of the research will contribute to the research, because only recently all the experimental components have been developed to the degree that they enable such experiments, and therefore the community is quite receptive to these ideas. Indeed, several leading laboratories are working in the area, and that will maximise the relevance of our findings to their experiments. In the UK there is a strong community working in various areas and systems of quantum optics, as well as a small but very advanced community working in the area of high coherence superconducting devices.

Technological innovation and public sector

We have many mathematically beautiful results in quantum field theory of condensed matter, and amazing measurements with extremely clean and meticulously designed micro and nano structures. Quantum technology is built around the narrative of applying such purely academic knowledge and expertise to useful applications. This proposal is built on one hand around achieving academic excellence, but at the same time it is geared towards implementing theory directly with devices that are considered one of the leading technologies for realising 'quantum machines'. Indeed, several industrial bodies see the opportunity and have already become stake-holders in this technology, for instance IBM, BBN Raytheon, D-Wave (with Google, NASA and Lockheed Martin as customers), and several national research laboratories heavily involved, though they still heavily rely on national research funds at the moment. In the short term, these industry ventures are recruiting from universities, so there is a flow of ideas from us, the academic research groups, to the industry that influences their directions of research. For example IBM Research at Watson have adopted and merged qubit architecture ideas from both UCSB and Yale since these are the places where their personnel came from. We believe the beyond that, the research that we propose here could be applied directly to their efforts, since they are aiming at scaling up their existing quantum superconducting microprocessors and we aim to develop ideas regarding quantum networks that can be an integral part of such a device or link several. Importantly, these proto-industrial activities which are carried out in several scientifically leading countries, create opportunities for our PhD students to go for postdoctoral training, and they return with the added expertise to the UK. In the longer term large industry investments will need to happen in order to make commercial technology. We can see this is beginning to happen with D-Wave and eventually as a sector we should aim to attract venture capital to the UK. For this to happen we need to create research that attracts a fund like Quantum Wave Fund that specialises in quantum technologies to invest in the UK (currently it invests in companies in the US, Switzerland and Estonia). In the UK there are governmental bodies that have an interest in quantum engineering such as GCHQ and MoD for quantum cryptography and accurate navigation and sensing, respectively. Other public bodies such as the Met office are a major potential users of future efficient large scale quantum computing resources, and the financial sector is another.