ORCID Profile
0000-0002-5089-3148
Current Organisation
Heriot-Watt University
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Quantum Physics | Quantum Optics | Quantum Information, Computation and Communication | Nonlinear Optics and Spectroscopy |
Expanding Knowledge in the Physical Sciences | Emerging Defence Technologies | Expanding Knowledge in Engineering | Expanding Knowledge in Technology
Publisher: Springer Science and Business Media LLC
Date: 03-02-2022
DOI: 10.1038/S41534-022-00520-8
Abstract: Efficient distributed computing offers a scalable strategy for solving resource-demanding tasks, such as parallel computation and circuit optimisation. Crucially, the communication overhead introduced by the allotment process should be minimised—a key motivation behind the communication complexity problem (CCP). Quantum resources are well-suited to this task, offering clear strategies that can outperform classical counterparts. Furthermore, the connection between quantum CCPs and non-locality provides an information-theoretic insight into fundamental quantum mechanics. Here we connect quantum CCPs with a generalised non-locality framework—beyond Bell’s paradigmatic theorem—by incorporating the underlying causal structure, which governs the distributed task, into a so-called non-local hidden-variable model. We prove that a new class of communication complexity tasks can be associated with Bell-like inequalities, whose violation is both necessary and sufficient for a quantum gain. We experimentally implement a multipartite CCP akin to the guess-your-neighbour-input scenario, and demonstrate a quantum advantage when multipartite Greenberger-Horne-Zeilinger (GHZ) states are shared among three users.
Publisher: AIP Publishing
Date: 06-2022
DOI: 10.1063/5.0089313
Abstract: Frequency encoding is quickly becoming an attractive prospect for quantum information protocols owing to larger Hilbert spaces and increased resilience to noise compared to other photonic degrees of freedom. To fully make use of frequency encoding as a practical paradigm for quantum information processing, an efficient and simple source of frequency entanglement is required. Here, we present a single-pass source of discrete frequency-bin entanglement that does not use filtering or a resonant cavity. We use a domain-engineered nonlinear crystal to generate an eight-mode frequency-bin entangled source at telecommunication wavelengths. Our approach leverages the high heralding efficiency and simplicity associated with bulk crystal sources.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-08-2016
Abstract: Causation at a distance does not explain quantum correlations.
Publisher: American Physical Society (APS)
Date: 16-12-2009
Publisher: American Physical Society (APS)
Date: 02-01-2020
Publisher: IOP Publishing
Date: 11-08-2010
Publisher: AIP Publishing
Date: 26-04-2021
DOI: 10.1063/5.0045413
Abstract: On-demand indistinguishable single-photon sources are essential for quantum networking and communication. Semiconductor quantum dots are among the most promising candidates, but their typical emission wavelength renders them unsuitable for use in fiber networks. Here, we present quantum frequency conversion of near-infrared photons from a bright quantum dot to the telecommunication C-band, allowing integration with existing fiber architectures. We use a custom-built, tunable 2400 nm seed laser to convert single photons from 942 nm to 1550 nm in a difference-frequency generation process. We achieve an end-to-end conversion efficiency of ≃35%, demonstrate count rates approaching 1 MHz at 1550 nm with g(2)(0)=0.043(1), and achieve Hong-Ou-Mandel (HOM) visibilities of 60%. We expect this scheme to be preferable to quantum dot sources directly emitting at telecom wavelengths for fiber-based quantum networking.
Publisher: World Scientific Pub Co Pte Lt
Date: 03-2005
DOI: 10.1142/S0219749905000797
Abstract: In this work we review the security vulnerability of quantum cryptography with respect to "man-in-the-middle attacks" and the standard authentication methods applied to counteract these attacks. We further propose a modified authentication algorithm which features higher efficiency with respect to consumption of mutual secret bits.
Publisher: IEEE
Date: 05-2011
Publisher: The Optical Society
Date: 26-10-2011
DOI: 10.1364/OE.19.022698
Publisher: American Association for the Advancement of Science (AAAS)
Date: 04-06-2021
Abstract: When Alice and Bob invite their friends, quantum key distribution with multiparty entanglement enables secure conference call.
Publisher: Proceedings of the National Academy of Sciences
Date: 03-01-2013
Abstract: The counterintuitive features of quantum physics challenge many common-sense assumptions. In an interferometric quantum eraser experiment, one can actively choose whether or not to erase which-path information (a particle feature) of one quantum system and thus observe its wave feature via interference or not by performing a suitable measurement on a distant quantum system entangled with it. In all experiments performed to date, this choice took place either in the past or, in some delayed-choice arrangements, in the future of the interference. Thus, in principle, physical communications between choice and interference were not excluded. Here, we report a quantum eraser experiment in which, by enforcing Einstein locality, no such communication is possible. This is achieved by independent active choices, which are space-like separated from the interference. Our setup employs hybrid path-polarization entangled photon pairs, which are distributed over an optical fiber link of 55 m in one experiment, or over a free-space link of 144 km in another. No naive realistic picture is compatible with our results because whether a quantum could be seen as showing particle- or wave-like behavior would depend on a causally disconnected choice. It is therefore suggestive to abandon such pictures altogether.
Publisher: American Physical Society (APS)
Date: 04-02-2020
Publisher: American Physical Society (APS)
Date: 20-05-2011
Publisher: IOP Publishing
Date: 04-08-2009
Publisher: IEEE
Date: 2005
Publisher: IOP Publishing
Date: 20-05-2011
Publisher: Springer Science and Business Media LLC
Date: 31-03-2022
DOI: 10.1038/S41598-022-08693-0
Abstract: The suggestion that quantum coherence might enhance biological processes such as photosynthesis is not only of fundamental importance but also leads to hopes of developing bio-inspired ‘green’ quantum technologies that mimic nature. A key question is how the timescale of coherent processes in molecular systems compare to that of the driving light source—the Sun. Across the quantum biology literature on light-harvesting, the coherence time quoted for sunlight spans about two orders of magnitude, ranging from 0.6 to ‘10s’ of femtoseconds. This difference can potentially be significant in deciding whether the induced light-matter coherence is long enough to affect dynamical processes following photoexcitation. Here we revisit the historic calculations of sunlight coherence starting with the black-body spectrum and then proceed to provide values for the more realistic case of atmospherically filtered light. We corroborate these values with interferometric measurements of the complex degree of temporal coherence from which we calculate the coherence time of atmospherically filtered sunlight as $$1.12\\pm {0.04}\\,{\\hbox { fs}}$$ 1.12 ± 0.04 fs , as well as the coherence time in a chlorophyll analogous filtered case as $$4.87\\pm {0.21}\\,{\\hbox { fs}}$$ 4.87 ± 0.21 fs .
Publisher: IEEE
Date: 09-2006
Publisher: Springer Science and Business Media LLC
Date: 03-05-2009
DOI: 10.1038/NPHYS1255
Publisher: AIP Publishing
Date: 19-07-2010
DOI: 10.1063/1.3460920
Abstract: We demonstrate the distribution of polarization entangled photons of wavelength 810 nm through standard telecom fibers. This technique allows quantum communication protocols to be performed over established fiber infrastructure, and makes use of the smaller and better performing setups available around 800 nm, as compared to those which use telecom wavelengths around 1550 nm. We examine the excitation and subsequent quenching of higher-order spatial modes in telecom fibers up to 6 km in length, and perform a distribution of high quality entanglement (visibility 95.6%). Finally, we demonstrate quantum key distribution using entangled 810 nm photons over a 4.4 km long installed telecom fiber link.
Publisher: Optica Publishing Group
Date: 02-03-2021
DOI: 10.1364/OE.416143
Abstract: Experimental quantum key distribution through free-space channels requires accurate pointing-and-tracking to co-align telescopes for efficient transmission. The hardware requirements for the sender and receiver could be drastically reduced by combining the detection of quantum bits and spatial tracking signal using two-dimensional single-photon detector arrays. Here, we apply a two-dimensional CMOS single-photon avalanche diode detector array to measure and monitor the single-photon level interference of a free-space time-bin receiver interferometer while simultaneously tracking the spatial position of the single-photon level signal. We verify an angular field-of-view of 1.28° and demonstrate a post-processing technique to reduce background noise. The experimental results show a promising future for two-dimensional single-photon detectors in low-light level free-space communications, such as quantum communications.
Publisher: Optica Publishing Group
Date: 2007
DOI: 10.1364/OE.15.015377
Abstract: We demonstrate a wavelength-tunable, fiber-coupled source of polarization- entangled photons with extremely high spectral brightness and quality of entanglement. Using a 25 mm PPKTP crystal inside a polarization Sagnac interferometer we detect a spectral brightness of 273000 pairs (s mW nm)(-1), a factor of 28 better than comparable previous sources while state tomography showed the two-photon state to have a tangle of T = 0.987. This improvement was achieved by use of a long crystal, careful selection of focusing parameters and single-mode fiber coupling. We demonstrate that, due to the particular geometry of the setup, the signal and idler wavelengths can be tuned over a wide range without loss of entanglement.
Publisher: The Optical Society
Date: 12-11-2018
Publisher: Informa UK Limited
Date: 10-05-2012
Publisher: Proceedings of the National Academy of Sciences
Date: 11-2010
Abstract: Bell’s theorem shows that local realistic theories place strong restrictions on observable correlations between different systems, giving rise to Bell’s inequality which can be violated in experiments using entangled quantum states. Bell’s theorem is based on the assumptions of realism, locality, and the freedom to choose between measurement settings. In experimental tests, “loopholes” arise which allow observed violations to still be explained by local realistic theories. Violating Bell’s inequality while simultaneously closing all such loopholes is one of the most significant still open challenges in fundamental physics today. In this paper, we present an experiment that violates Bell’s inequality while simultaneously closing the locality loophole and addressing the freedom-of-choice loophole, also closing the latter within a reasonable set of assumptions. We also explain that the locality and freedom-of-choice loopholes can be closed only within nondeterminism, i.e., in the context of stochastic local realism.
Publisher: Springer Science and Business Media LLC
Date: 07-2010
DOI: 10.1038/NATURE09175
Abstract: Non-classical states of light, such as entangled photon pairs and number states, are essential for fundamental tests of quantum mechanics and optical quantum technologies. The most widespread technique for creating these quantum resources is spontaneous parametric down-conversion of laser light into photon pairs. Conservation of energy and momentum in this process, known as phase-matching, gives rise to strong correlations that are used to produce two-photon entanglement in various degrees of freedom. It has been a longstanding goal in quantum optics to realize a source that can produce analogous correlations in photon triplets, but of the many approaches considered, none has been technically feasible. Here we report the observation of photon triplets generated by cascaded down-conversion. Each triplet originates from a single pump photon, and therefore quantum correlations will extend over all three photons in a way not achievable with independently created photon pairs. Our photon-triplet source will allow experimental interrogation of novel quantum correlations, the generation of tripartite entanglement without post-selection and the generation of heralded entangled photon pairs suitable for linear optical quantum computing. Two of the triplet photons have a wavelength matched for optimal transmission in optical fibres, suitable for three-party quantum communication. Furthermore, our results open interesting regimes of non-linear optics, as we observe spontaneous down-conversion pumped by single photons, an interaction also highly relevant to optical quantum computing.
Publisher: Springer Science and Business Media LLC
Date: 22-08-2023
DOI: 10.1038/S41534-023-00750-4
Abstract: Quantum conference key agreement (QCKA) allows multiple users to establish a secure key from a shared multi-partite entangled state. In a quantum network, this protocol can be efficiently implemented using a single copy of a N-qubit Greenberger-Horne-Zeilinger (GHZ) state to distil a secure N-user conference key bit, whereas up to N-1 entanglement pairs are consumed in the traditional pair-wise protocol. We demonstrate the advantage provided by GHZ states in a testbed consisting of a photonic six-user quantum network, where four users can distil either a GHZ state or the required number of Bell pairs for QCKA using network routing techniques. In the asymptotic limit, we report a more than two-fold enhancement of the conference key rate when comparing the two protocols. We extrapolate our data set to show that the resource advantage for the GHZ protocol persists when taking into account finite-key effects.
Publisher: Springer Science and Business Media LLC
Date: 02-08-2018
DOI: 10.1038/S41534-018-0086-Y
Abstract: Multipartite quantum correlations are a powerful resource that underpins applications from quantum metrology to quantum computing. While most research has focused on spatial correlations, it is now becoming clear that a sequence of measurements on a single quantum system at different points in time reveals a similarly rich, yet fundamentally different structure of multipartite temporal correlations. Here we experimentally observe genuine multi-time correlations in a sequence of three generalized measurements on a single photon. These correlations, manifest by a simultaneous violation of all pairwise Bell inequalities, cannot be reproduced by any spatial quantum state of equal dimension. Our work lays the foundation for the exploration of temporal correlations arising in quantum networks for quantum information applications.
Publisher: IEEE
Date: 06-2009
Publisher: The Optical Society
Date: 20-12-2011
DOI: 10.1364/OE.19.000055
Publisher: Springer Science and Business Media LLC
Date: 06-06-2012
DOI: 10.1038/NCOMMS1872
Abstract: Topological phases exhibit some of the most striking phenomena in modern physics. Much of the rich behaviour of quantum Hall systems, topological insulators, and topological superconductors can be traced to the existence of robust bound states at interfaces between different topological phases. This robustness has applications in metrology and holds promise for future uses in quantum computing. Engineered quantum systems--notably in photonics, where wavefunctions can be observed directly--provide versatile platforms for creating and probing a variety of topological phases. Here we use photonic quantum walks to observe bound states between systems with different bulk topological properties and demonstrate their robustness to perturbations--a signature of topological protection. Although such bound states are usually discussed for static (time-independent) systems, here we demonstrate their existence in an explicitly time-dependent situation. Moreover, we discover a new phenomenon: a topologically protected pair of bound states unique to periodically driven systems.
Publisher: IEEE
Date: 06-2009
Publisher: American Physical Society (APS)
Date: 15-06-2020
Publisher: Optica Publishing Group
Date: 04-10-2023
DOI: 10.1364/OE.494070
Publisher: Springer Science and Business Media LLC
Date: 10-01-2012
DOI: 10.1038/NCOMMS1628
Publisher: Optica Publishing Group
Date: 19-02-2021
DOI: 10.1364/OE.416843
Abstract: The ideal photon-pair source for building up multi-qubit states needs to produce indistinguishable photons with high efficiency. Indistinguishability is crucial for minimising errors in two-photon interference, central to building larger states, while high heralding rates will be needed to overcome unfavourable loss scaling. Domain engineering in parametric down-conversion sources negates the need for lossy spectral filtering allowing one to satisfy these conditions inherently within the source design. Here, we present a telecom-wavelength parametric down-conversion photon source that operates on the achievable limit of domain engineering. We generate photons from independent sources which achieve two-photon interference visibilities of up to 98.6 ± 1.1% without narrow-band filtering. As a consequence, we reach net heralding efficiencies of up to 67.5%, which corresponds to collection efficiencies exceeding 90%.
Publisher: American Physical Society (APS)
Date: 21-11-2007
Publisher: World Scientific Pub Co Pte Lt
Date: 10-2009
DOI: 10.1142/S0219749909005729
Abstract: In this work, we respond to a comment by A. Abidin and J.-Å. Larsson on our previous paper, Int. J. Quant. Inf.3 (2005) 225.
Publisher: The Optical Society
Date: 15-03-2019
DOI: 10.1364/OE.27.009258
Publisher: American Association for the Advancement of Science (AAAS)
Date: 20-12-2013
Abstract: Quantum computers are unnecessary for exponentially efficient computation or simulation if the Extended Church-Turing thesis is correct. The thesis would be strongly contradicted by physical devices that efficiently perform tasks believed to be intractable for classical computers. Such a task is boson s ling: s ling the output distributions of n bosons scattered by some passive, linear unitary process. We tested the central premise of boson s ling, experimentally verifying that three-photon scattering litudes are given by the permanents of submatrices generated from a unitary describing a six-mode integrated optical circuit. We find the protocol to be robust, working even with the unavoidable effects of photon loss, non-ideal sources, and imperfect detection. Scaling this to large numbers of photons should be a much simpler task than building a universal quantum computer.
Publisher: IOP Publishing
Date: 27-10-2009
Publisher: IEEE
Date: 2005
Publisher: American Physical Society (APS)
Date: 16-04-2010
Publisher: Springer Science and Business Media LLC
Date: 16-06-2023
DOI: 10.1038/S41467-023-39219-5
Abstract: Quantum key distribution with solid-state single-photon emitters is gaining traction due to their rapidly improving performance and compatibility with future quantum networks. Here we emulate a quantum key distribution scheme with quantum-dot-generated single photons frequency-converted to 1550 nm, achieving count rates of 1.6 MHz with $${g}^{\\left(2\\right)}\\left(0\\right)=3.6\\%$$ g 2 0 = 3.6 % and asymptotic positive key rates over 175 km of telecom fibre. We show that the commonly used finite-key analysis for non-decoy state QKD drastically overestimates secure key acquisition times due to overly loose bounds on statistical fluctuations. Using the tighter multiplicative Chernoff bound to constrain the estimated finite key parameters, we reduce the required number of received signals by a factor 10 8 . The resulting finite key rate approaches the asymptotic limit at all achievable distances in acquisition times of one hour, and at 100 km we generate finite keys at 13 kbps for one minute of acquisition. This result is an important step towards long-distance single-emitter quantum networking.
Publisher: American Physical Society (APS)
Date: 30-01-2012
Publisher: American Association for the Advancement of Science (AAAS)
Date: 06-09-2019
Abstract: In the quantum domain, there may not be an objective story to tell.
Publisher: Springer Science and Business Media LLC
Date: 15-04-2016
DOI: 10.1038/NCOMMS11282
Abstract: Transport phenomena on a quantum scale appear in a variety of systems, ranging from photosynthetic complexes to engineered quantum devices. It has been predicted that the efficiency of coherent transport can be enhanced through dynamic interaction between the system and a noisy environment. We report an experimental simulation of environment-assisted coherent transport, using an engineered network of laser-written waveguides, with relative energies and inter-waveguide couplings tailored to yield the desired Hamiltonian. Controllable-strength decoherence is simulated by broadening the bandwidth of the input illumination, yielding a significant increase in transport efficiency relative to the narrowband case. We show integrated optics to be suitable for simulating specific target Hamiltonians as well as open quantum systems with controllable loss and decoherence.
Publisher: IEEE
Date: 06-2007
Publisher: American Physical Society (APS)
Date: 07-03-2011
Publisher: IEEE
Date: 05-2011
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2013
End Date: 09-2015
Amount: $375,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2018
End Date: 06-2025
Amount: $31,900,000.00
Funder: Australian Research Council
View Funded Activity