Experimentally generating and tuning robust entanglement between photonic qubits

We generate and study the entanglement properties of novel states composed of three polarisation-encoded photonic qubits. By varying a single experimental parameter we can coherently move from a fully separable state to a maximally robust W state, while at all times preserving an optimally robust, symmetric entanglement configuration. We achieve a high fidelity with these configurations experimentally, including the highest reported W state fidelity.Comment: lower print quality for arxiv figure

Manipulating biphotonic qutrits

Quantum information carriers with higher dimension than the canonical qubit offer significant advantages. However, manipulating such systems is extremely difficult. We show how measurement induced non-linearities can be employed to dramatically extend the range of possible transforms on biphotonic qutrits; the three level quantum systems formed by the polarisation of two photons in the same spatio-temporal mode. We fully characterise the biphoton-photon entanglement that underpins our technique, thereby realising the first instance of qubit-qutrit entanglement. We discuss an extension of our technique to generate qutrit-qutrit entanglement and to manipulate any bosonic encoding of quantum information.Comment: 4 pages, 4 figure

Demonstration of a simple entangling optical gate and its use in Bell-state analysis

We demonstrate a new architecture for an optical entangling gate that is significantly simpler than previous realisations, using partially-polarising beamsplitters so that only a single optical mode-matching condition is required. We demonstrate operation of a controlled-Z gate in both continuous-wave and pulsed regimes of operation, fully characterising it in each case using quantum process tomography. We also demonstrate a fully-resolving, nondeterministic optical Bell-state analyser based on this controlled-Z gate. This new architecture is ideally suited to guided optics implementations of optical gates.Comment: 4 pages, 3 figures. v2: additional author, improved data and figures (low res), some other minor changes. Accepted for publication in PR

Quantum process tomography of a controlled-NOT gate

We demonstrate complete characterization of a two-qubit entangling process - a linear optics controlled-NOT gate operating with coincident detection - by quantum process tomography. We use maximum-likelihood estimation to convert the experimental data into a physical process matrix. The process matrix allows accurate prediction of the operation of the gate for arbitrary input states, and calculation of gate performance measures such as the average gate fidelity, average purity and entangling capability of our gate, which are 0.90, 0.83 and 0.73, respectively.Comment: 4 pages, 2 figures. v2 contains new data corresponding to improved gate operation. Figure quality slightly reduced for arXi

Experimental demonstration of Shor's algorithm with quantum entanglement

Shor's powerful quantum algorithm for factoring represents a major challenge in quantum computation and its full realization will have a large impact on modern cryptography. Here we implement a compiled version of Shor's algorithm in a photonic system using single photons and employing the non-linearity induced by measurement. For the first time we demonstrate the core processes, coherent control, and resultant entangled states that are required in a full-scale implementation of Shor's algorithm. Demonstration of these processes is a necessary step on the path towards a full implementation of Shor's algorithm and scalable quantum computing. Our results highlight that the performance of a quantum algorithm is not the same as performance of the underlying quantum circuit, and stress the importance of developing techniques for characterising quantum algorithms.Comment: 4 pages, 5 figures + half-page additional online materia

Integrated Photonic Sensing

Loss is a critical roadblock to achieving photonic quantum-enhanced technologies. We explore a modular platform for implementing integrated photonics experiments and consider the effects of loss at different stages of these experiments, including state preparation, manipulation and measurement. We frame our discussion mainly in the context of quantum sensing and focus particularly on the use of loss-tolerant Holland-Burnett states for optical phase estimation. In particular, we discuss spontaneous four-wave mixing in standard birefringent fibre as a source of pure, heralded single photons and present methods of optimising such sources. We also outline a route to programmable circuits which allow the control of photonic interactions even in the presence of fabrication imperfections and describe a ratiometric characterisation method for beam splitters which allows the characterisation of complex circuits without the need for full process tomography. Finally, we present a framework for performing state tomography on heralded states using lossy measurement devices. This is motivated by a calculation of the effects of fabrication imperfections on precision measurement using Holland-Burnett states.Comment: 19 pages, 7 figure

a pilot randomized controlled trial

Objectives: Our primary aim of this pilot study was to test feasibility of the planned design, the interventions (education plus telephone coaching), and the outcome measures, and to facilitate a power calculation for a future randomized controlled trial to improve adherence to recovery goals following hip fracture. Design: This is a parallel 1:1 randomized controlled feasibility study. Setting: The study was conducted in a teaching hospital in Vancouver, BC, Canada. Participants: Participants were community-dwelling adults over 60 years of age with a recent hip fracture. They were recruited and assessed in hospital, and then randomized after hospital discharge to the intervention or control group by a web-based randomization service. Treatment allocation was concealed to the investigators, measurement team, and data entry assistants and analysts. Participants and the research physiotherapist were aware of treatment allocation. Intervention: Intervention included usual care for hip fracture plus a 1-hour in-hospital educational session using a patient- centered educational manual and four videos, and up to five postdischarge telephone calls from a physiotherapist to provide recovery coaching. The control group received usual care plus a 1-hour in-hospital educational session using the educational manual and videos. Measurement: Our primary outcome was feasibility, specifically recruitment and retention of participants. We also collected selected health outcomes, including health- related quality of life (EQ5D-5L), gait speed, and psychosocial factors (ICEpop CAPability measure for Older people and the Hospital Anxiety and Depression Scale). Results: Our pilot study results indicate that it is feasible to recruit, retain, and provide follow-up telephone coaching to older adults after hip fracture. We enrolled 30 older adults (mean age 81.5 years; range 61–97 years), representing a 42% recruitment rate. Participants excluded were those who were not community dwelling on admission, were discharged to a residential care facility, had physician-diagnosed dementia, and/or had medical contraindications to participation. There were 27 participants who completed the study: eleven in the intervention group, 15 in the control group, and one participant completed a qualitative interview only. There were no differences between groups for health measures. Conclusion: We highlight the feasibility of telephone coaching for older adults after hip fracture to improve adherence to mobility recovery goals

Quantum teleportation and entanglement swapping with linear optics logic gates

We report on the usage of a linear optics phase gate for distinguishing all four Bell states simultaneously in a quantum teleportation and entanglement swapping protocol. This is demonstrated by full state tomography of the one and two qubit output states of the two protocols, yielding average state fidelities of about 0.83 and 0.77, respectively. In addition, the performance of the teleportation channel is characterised by quantum process tomography. The non classical properties of the entanglement swapping output states are further confirmed by the violation of a CHSH-type Bell inequality of 2.14 on average.Comment: 11 pages, 3 figure