16 research outputs found
Hyper-entanglement between pulse modes and frequency bins
Hyper-entanglement between two or more photonic degrees of freedom (DOF) can
enhance and enable new quantum protocols by allowing each DOF to perform the
task it is optimally suited for. Here we demonstrate the generation of photon
pairs hyper-entangled between pulse modes and frequency bins. The pulse modes
are generated via parametric downconversion in a domain-engineered crystal and
subsequently entangled to two frequency bins via a spectral mapping technique.
The resulting hyper-entangled state is characterized and verified via
measurement of its joint spectral intensity and non-classical two-photon
interference patterns from which we infer its spectral phase. The protocol
combines the robustness to loss, intrinsic high dimensionality and
compatibility with standard fiber-optic networks of the energy-time DOF with
the ability of hyper-entanglement to increase the capacity and efficiency of
the quantum channel, already exploited in recent experimental applications in
both quantum information and quantum computation
Quantum communication complexity beyond Bell nonlocality
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 nonlocality provides an
information-theoretic insights into fundamental quantum mechanics. Here we
connect quantum CCPs with a generalised nonlocality framework -- beyond the
paradigmatic Bell's theorem -- by incorporating the underlying causal
structure, which governs the distributed task, into a so-called nonlocal hidden
variable model. We prove that a new class of communication complexity tasks can
be associated to 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.Comment: 21 pages, 5 figure
Frequency-bin entanglement from domain-engineered down-conversion
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 QIP, an efficient and simple
source of frequency entanglement is required. Here we present a single-pass
source of discrete frequency-bin entanglement which 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 efficient and simplicity associated with
bulk crystal sources.Comment: 6 pages, 4 figure
Optimised domain-engineered crystals for pure telecom photon sources
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
without narrow-band filtering. As a consequence, we reach net
heralding efficiencies of up to , which corresponds to collection
efficiencies exceeding .Comment: 6 pages, 5 figures, 1 page of supplementar
Conference key agreement in a quantum network
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
Experimental network advantage for quantum conference key agreement
One of the great promises of quantum technology is the development of quantum
networks, which will allow global distribution of entanglement for tasks such
as distributed quantum computing, distributed quantum sensing and
quantum-secure communication. To leverage the full potential of quantum
networks we require protocols that draw an efficiency advantage from genuine
multi-partite entanglement as opposed to strictly pair-wise correlations such
as Bell states. Multi-user entanglement such as Greenberger-Horne-Zeilinger
(GHZ) states have already found application in quantum conference key
agreement, quantum secret sharing and quantum communication complexity
problems. However, a true network advantage has not yet been achieved. In this
work we create a six-photon graph-state network from which we derive either a
four-user GHZ state for direct quantum conference key agreement or the required
amount of Bell pairs for the equivalent pair-wise protocol. We show that the
GHZ-state protocol has a more than two-fold rate advantage by only consuming
half the amount of network resources per secure conference key bit
Entanglement-based quantum communication complexity beyond Bell nonlocality
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 nonlocality provides an
information-theoretic insights into fundamental quantum mechanics. Here we
connect quantum CCPs with a generalised nonlocality framework -- beyond the
paradigmatic Bell's theorem -- by incorporating the underlying causal
structure, which governs the distributed task, into a so-called nonlocal hidden
variable model. We prove that a new class of communication complexity tasks can
be associated to 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.Comment: 21 pages, 5 figure