Quantum Coherence: Joint Proposal for Optimising UK Research Capacity and Capability

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics


The defining character of quantum mechanics is coherence / the superposition of correlated states of many particles. Quantum correlated and entangled states lie at the heart of several major areas of physics, especially quantum optics, atomic physics and quantum condensed matter. The ability to control precisely a broad range of systems from ultracold atoms in optical lattices to internal states of molecules to semiconductor nanostructures has led to important breakthroughs in the understanding and potential applications of entanglement. Because the same principles underlie the rich but sometimes impenetrable physics of quantum matter, these advances open a window on challenging problems in materials. The fortunate fertility already evident in condensed matter materials suggests strongly that major benefits will accrue from exerting full quantum control of complex systems. Within this proposal we shall tackle this demanding new challenge. The underlying concepts and technologies of coherent control and manipulation in atomic, molecular and optical physics are now sufficiently established that it is possible to consider the synthesis of designer quantum states of atoms and molecules that can address a number of outstanding problems in condensed matter and optical physics. Furthermore, the ability to build large-scale quantum coherent systems represents such a new capability that we can anticipate new physics, as yet unimagined, as well as new technologies, to emerge. The method of approach will be to increase UK research capacity by the appointment of new faculty and the establishment of state of the art research laboratories and facilities, and the nurturing of collaborative research programs across several institutions. This will be complemented by implementing new training programs at the graduate and postdoctoral researcher level that will be broadly available to the UK community.
Description This grant supported the early research of Brian Smith and David Lucas
1. Quantum optics: BJ Smith and IA Walmsley
The major research findings in the area of quantum optics at Oxford have concerned the development of devices and methods for the implementation of quantum photonic networks. Specific accomplishments have been: the preparation of the world's purest single photon states by means of nonlinear optics; framing the concept and the first demonstration of weak-field homodyne detection as a non-Gaussian measurement; the first demonstration of full quantum tomography of measurement for photodetectors; one of the two first demonstrations of controllable nonclassical interference on a photonic chip; the optimisation and demonstration of quantum metrology including photon loss for real-world sensors; the first demonstration of multi-photon interference on a photonic chip, and its first application to a quantum algorithm - Boson Sampling.
2. Trapped atomic and ionic matter: D Lucas
In 2007 a memory coherence of a single qubit after 1 second of >98%, was achieved - the longest-lived single qubit reported, until our 2012 result. This was followed in 2008 by our reporting the first qubit operation (readout) above the 99.99% fidelity threshold (long considered to be the threshold necessary for fault-tolerant quantum computing). We also achieved, in 2009, the first measurement of coherence of a sympathetically-cooled memory qubit. Further work in 2010 extended the 99.99% qubit readout to multiple qubits, tackling qubit-qubit cross-talk error. In addition we achieved the first demonstration outside the US of a microfabricated surface-electrode ion trap - a key technology for scaling to many qubits. In 2011 we reported the first demonstration of reduction of "anomalous heating" in an ion trap by removal of noise source (in this case by cleaning with a pulsed laser). Finally in 2012 we achieved the first demonstration of a microfabricated trap with integrated microwave circuitry and the first all single-qubit operations at fault-tolerant levels: state preparation and readout at 99.97% fidelity, memory with 50-second lifetime, gates at 99.9999% fidelity.
3. Attoscience: IA Walmsley and AS Wyatt
We have built a source of attosecond XUV pulses based on high harmonic generation (HHG) from a few-cycle visible driving laser. Key developments include increasing the accuracy and precision of optical metrology for the driving laser to enable accurate and precise control of the optical waveform leading to shaping and optimization of the XUV generation process enabling all-optical characterization schemes to be used to fully reconstruct the full space-time XUV field. Techniques that we have developed include XUV lateral shearing interferometery (LSI), enabling the direct reconstruction of space-time coupling of XUV attosecond pulses; XUV spectral phase interferometry for direct electric-field reconstruction (SPIDER) to enable complete temporal characterization of attosecond pulses; vectorial phase retrieval for complete spatial and temporal characterization of XUV attosecond pulses; and developed methods to study quantum path interference in HHG, enabling the quantum dynamics of the HHG process to be studied.
In addition to generating XUV attosecond pulses, we have been developing methods to generate intense arbitrary waveforms based on coherent molecular moduation to be used as pump pulses in pump-probe experiments. Due to the nature of these pulses, we have developed novel characterization methods that enable the full waveform of an arbitrary pulse to be measured. Other developments include improvements in conventional ultrafast technology.
Exploitation Route The research results are already being used in future grants
Sectors Digital/Communication/Information Technologies (including Software),Electronics,Other