arXiv subjects

Jacob A. Dunningham

Publications and source records attributed to Jacob A. Dunningham.

14 recordsLinked to original sources

arXiv2026

Enhanced quantum metrology with robust multipass interferometry

Quantum metrology typically uses entangled states to achieve measurement precisions beyond the standard quantum limit. The advantage increases with the size of the entangled state, however generating and preserving large entangled states remains a major experimental challenge. Multipass protocols offer an alternative approach by allowing a single probe to interact repeatedly with the parameter of interest, but their performance is highly susceptible to loss, which accumulates over successive passes and rapidly erodes the quantum advantage. Here we introduce a hybrid strategy that combines small, loss-resilient entangled states with multipass interferometry. We show that this approach retains the robustness of small entangled probes while exploiting repeated interactions to achieve substantial enhancements in measurement precision. Furthermore, we propose a concrete implementation using currently available technologies, demonstrating that the predicted performance gains should be experimentally accessible with existing capabilities.

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arXiv2026

James-Stein estimation for quantum sensing schemes

Quantum metrology protocols typically consist of four steps: state preparation, evolution, measurement, and data processing. Often, the first three steps are prioritised when designing a scheme as they contain all the quantum elements. The data analysis is generally considered an add-on with an implicit assumption that this step is well behaved and so standard data techniques can be applied. However, the situation can be more nuanced, such as when the available data are limited. In limited-data quantum metrology the choice of data analysis technique and cost function of the estimator is of great importance, and a reliable prior distribution of the unknown parameters is required for Bayesian analysis. An interesting question is what we should do when no such prior is available. In this work, we consider how the James-Stein estimator can give significant advantages when measuring multiple unknown parameters with limited data and, importantly, does not require any prior distribution. We demonstrate the advantage by applying this methodology to simple quantum metrology schemes.

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arXiv2024

Robustness of entanglement in a non-Hermitian cavity-optomechanical system even away from exceptional points

Quantum physics can be extended into the complex domain by considering non-Hermitian Hamiltonians that are $\mathcal{PT}$-symmetric. These exhibit exceptional points (EPs) where the eigenspectrum changes from purely real to purely imaginary values and have useful properties enabling applications such as accelerated entanglement generation and the delay of the sudden death of entanglement in noisy systems. An interesting question is whether similar beneficial effects can be achieved away from EPs, since this would extend the available parameter space and make experiments more accessible. We investigate this by considering a $\mathcal{PT}$-symmetric optomechanical system but also consider what happens when two-mode squeezing interactions are included, taking us into the pseudo-Hermitian regime. The addition of squeezing is motivated by an attempt to extend the lifetime of the system's entanglement. While this does not prove to be the case, rich dynamics are nonetheless observed in both the pseudo-Hermitian and $\mathcal{PT}$-symmetric systems, including the sudden death and revival of entanglement under certain conditions. In both cases, we find that the sudden disappearance of entanglement can be mitigated at EPs, and also show that the revival of entanglement is quite robust to thermal noise in a group of parameters away from the EPs. This investigation extends our understanding of non-Hermitian systems and opens a new perspective for the development of quantum devices in non-Hermitian systems even away from EPs.

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arXiv2024

Secure quantum-enhanced measurements on a network of sensors

Two-party secure quantum remote sensing (SQRS) protocols enable quantum-enhanced measurements at remote locations with guaranteed security against eavesdroppers. This idea can be scaled up to networks of nodes where one party can directly measure functions of parameters at the different nodes using entangled states. However, the security on such networks decreases exponentially with the number of nodes. Here we show how this problem can be overcome in a hybrid protocol that utilises both entangled and separable states to achieve quantum-enhanced measurement precision and security on networks of any size.

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arXiv2020

Spin Squeezing of a Bose-Einstein Condensate via Quantum Non-Demolition Measurement for Quantum-Enhanced Atom Interferometry

We theoretically investigate the use of quantum non-demolition measurement to enhance the sensitivity of atom interferometry with Bose-condensed atoms. In particular, we are concerned with enhancing existing high-precision atom interferometry apparatuses, so restrict ourselves to dilute atomic samples, and the use of free-propagating light, or optical cavities in the weak-coupling regime. We find the optimum parameter regime that balances between spin squeezing and atomic loss, and find that significant improvements in sensitivity are possible. Finally, we consider the use of squeezed light, and show that this can provide further boosts to sensitivity.

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arXiv2018

Optimal Matterwave Gravimetry

We calculate quantum and classical Fisher informations for gravity sensors based on matterwave interference, and find that current Mach-Zehnder interferometry is not optimally extracting the full metrological potential of these sensors. We show that by making measurements that resolve either the momentum or the position we can considerably improve the sensitivity. We also provide a simple modification that is capable of more than doubling the sensitivity.

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arXiv2017

Heisenberg scaling with classical long-range correlations

The Heisenberg scaling is typically associated with nonclassicality and entanglement. In this work, however, we discuss how classical long-range correlations between lattice sites in many-body systems may lead to a 1/N scaling in precision with the number of probes. In particular, we show that networks of coupled single qubit lasers can be mapped onto a classical XY model, and a Heisenberg scaling with the number of sites appears when estimating the amplitude and phase of a weak periodic driving field.

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arXiv2017

Multi-parameter estimation in networked quantum sensors

We introduce a general model for a network of quantum sensors, and we use this model to consider the question: When can entanglement between the sensors, and/or global measurements, enhance the precision with which the network can measure a set of unknown parameters? We rigorously answer this question by presenting precise theorems proving that for a broad class of problems there is, at most, a very limited intrinsic advantage to using entangled states or global measurements. Moreover, for many estimation problems separable states and local measurements are optimal, and can achieve the ultimate quantum limit on the estimation uncertainty. This immediately implies that there are broad conditions under which simultaneous estimation of multiple parameters cannot outperform individual, independent estimations. Our results apply to any situation in which spatially localized sensors are unitarily encoded with independent parameters, such as when estimating multiple linear or non-linear optical phase shifts in quantum imaging, or when mapping out the spatial profile of an unknown magnetic field. We conclude by showing that entangling the sensors can enhance the estimation precision when the parameters of interest are global properties of the entire network.

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arXiv2016

One-parameter class of uncertainty relations based on entropy power

We use the concept of entropy power to derive a new one-parameter class of information-theoretic uncertainty relations for pairs of conjugate observables in an infinite-dimensional Hilbert space. This class constitutes an infinite tower of higher-order statistics uncertainty relations, which allows one in principle to determine the shape of the underlying information-distribution function by measuring the relevant entropy powers. We illustrate the capability of the new class by discussing two examples: superpositions of vacuum and squeezed states and the Cauchy-type heavy-tailed wave function.

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arXiv2014

On the Role of Information Theoretic Uncertainty Relations in Quantum Theory

Uncertainty relations based on information theory for both discrete and continuous distribution functions are briefly reviewed. We extend these results to account for (differential) Rényi entropy and its related entropy power. This allows us to find a new class of information-theoretic uncertainty relations (ITURs). The potency of such uncertainty relations in quantum mechanics is illustrated with a simple two-energy-level model where they outperform both the usual Robertson-Schrödinger uncertainty relation and Kraus-Maassen Shannon entropy based uncertainty relation. In the continuous case the ensuing entropy power uncertainty relations are discussed in the context of heavy tailed wave functions and Schrödinger cat states. Again, improvement over both the Robertson-Schrödinger uncertainty principle and Shannon ITUR is demonstrated in these cases. Further salient issues such as the proof of a generalized entropy power inequality and a geometric picture of information-theoretic uncertainty relations are also discussed.

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arXiv2014

Experimentally-driven approach for measuring quantum phase uncertainty

We propose a new generalised formalism for estimating the quantum phase uncertainty of pure and mixed continuous-variable quantum states and compare this with the phase uncertainty given by the quantum Fisher information. In order to preserve the Hermiticity of the operators, we use the Heisenberg and Schroedinger uncertainty relations to derive expressions for the phase uncertainty from generalised Susskind-Glogower operators. This formalism not only offers the possibility of directly measuring quantum phase uncertainties in a cavity-QED experiment but also gives a significant computational saving over the quantum Fisher information approach, which requires diagonalisation of the density matrix.

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arXiv2011

Behaviour of entanglement and Cooper pairs under relativistic boosts

Recent work has shown how single-particle entangled states are transformed when boosted in relativistic frames for certain restricted geometries. Here we extend that work to consider completely general inertial boosts. We then apply our single particle results to multiparticle entanglements by focussing on Cooper pairs of electrons. We show that a standard Cooper pair state consisting of a spin-singlet acquires spin-triplet components in a relativistically boosted inertial frame, regardless of the geometry. We also show that, if we start with a spin-triplet pair, two out of the three triplet states acquire a singlet component, the size of which depends on the geometry. This transformation between the different singlet and triplet superconducting pairs may lead to a better understanding of unconventional superconductivity.

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arXiv2010

Creating and observing N-partite entanglement with atoms

The Mermin inequality provides a criterion for experimentally ruling out local-realistic descriptions of multiparticle systems. A violation of this inequality means that the particles must be entangled, but does not, in general, indicate whether N-partite entanglement is present. For this, a stricter bound is required. Here we discuss this bound and use it to propose two different schemes for demonstrating N-partite entanglement with atoms. The first scheme involves Bose-Einstein condensates trapped in an optical lattice and the second uses Rydberg atoms in microwave cavities.

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arXiv2009

Scheme for implementing atomic multiport devices

Multiport generalizations of beam splitters are the key component in multipath interferometers, which are important in a range of quantum state engineering and precision measurement schemes. Here we propose a straightforward method for implementing multiport devices for atoms trapped in optical ring lattices. These devices are interesting as atoms have certain properties (such as mass) that photons do not and the ring configuration makes them useful for applications such as precision gyroscopes. We discuss how they could be employed in useful measurement schemes and investigate how practical considerations limit the size of the devices that can be achieved by this method.

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