Almut Beige | University of Leeds (original) (raw)

Papers by Almut Beige

arXiv (Cornell University), Jul 30, 2012

arXiv (Cornell University), Jun 15, 2010

arXiv (Cornell University), Jun 15, 2010

Cavity-mediated cooling has the potential to become one of the most efficient techniques to cool ... more Cavity-mediated cooling has the potential to become one of the most efficient techniques to cool molecular species down to very low temperatures. In this paper we analyse cavity cooling with single-laser driving for relatively large cavity decay rates kappa\kappakappa and relatively large phonon frequencies nu and show that it is essentially the same as ordinary laser cooling. This is done by calculating the stationary state phonon number mrmssm^{\rm ss}mrmss and the cooling rate gamma\gammagamma as a function of the system parameters. For example, when nu is either much larger or much smaller than kappa, the minimum stationary state phonon number scales as kappa^2/16nu^2 (strong confinement regime) and as kappa/4nu (weak confinement regime), respectively.

Nature Photonics, Apr 28, 2016

A double-slit experiment performed with two rubidium atoms precisely held in an optical lattice i... more A double-slit experiment performed with two rubidium atoms precisely held in an optical lattice inside an optical cavity provides a new platform for exploring quantum effects.

EPL, Jun 30, 2020

It is well known that quantum feedback can alter the dynamics of open quantum systems dramaticall... more It is well known that quantum feedback can alter the dynamics of open quantum systems dramatically. In this paper, we show that non-Ergodicity may be induced through quantum feedback and resultantly create system dynamics that have lasting dependence on initial conditions. To demonstrate this, we consider an optical cavity inside an instantaneous quantum feedback loop, which can be implemented relatively easily in the laboratory. Non-Ergodic quantum systems are of interest for applications in quantum information processing, quantum metrology and quantum sensing and could potentially aid the design of thermal machines whose efficiency is not limited by the laws of classical thermodynamics.

Sensors

One way of optically monitoring molecule concentrations is to utilise the high sensitivity of the... more One way of optically monitoring molecule concentrations is to utilise the high sensitivity of the transmission and reflection rates of Fabry-Pérot cavities to changes of their optical properties. Up to now, intrinsic and extrinsic Fabry-Pérot cavity sensors have been considered with analytes either being placed inside the resonator or coupled to evanescent fields on the outside. Here we demonstrate that Fabry-Pérot cavities can also be used to monitor molecule concentrations non-invasively and remotely, since the reflection of light from the target molecules back into the Fabry-Pérot cavity adds upwards peaks to the minima of its overall reflection rate. Detecting the amplitude of these peaks reveals information about molecule concentrations. By using an array of optical cavities, a wide range of frequencies can be probed at once and a unique optical fingerprint can be obtained.

arXiv (Cornell University), Aug 10, 2022

One way of optically monitoring molecule concentrations is to utilise the high sensitivity of the... more One way of optically monitoring molecule concentrations is to utilise the high sensitivity of the transmission and reflection rates of Fabry-Pérot cavities to changes of their optical properties. Up to now, intrinsic and extrinsic Fabry-Pérot cavity sensors have been considered with analytes either being placed inside the resonator or coupled to evanescent fields on the outside. Here we show that Fabry-Pérot cavities can also be used to monitor molecule concentrations non-invasively and remotely, since the reflection of light from the target molecules back into the Fabry-Pérot cavity adds upwards peaks to the minima of its overall reflection rate. Detecting the amplitude of these peaks reveals information about molecule concentrations. By using an array of optical cavities, a wide range of frequencies can be probed at once and a unique optical fingerprint can be obtained.

arXiv (Cornell University), Dec 5, 2011

Employing the fundamental laws of quantum physics, Quantum Key Distribution (QKD) promises the un... more Employing the fundamental laws of quantum physics, Quantum Key Distribution (QKD) promises the unconditionally secure distribution of cryptographic keys. However, in practical realisations, a QKD protocol is only secure, when the quantum bit error rate introduced by an eavesdropper unavoidably exceeds the system error rate. This condition guarantees that an eavesdropper cannot disguise his presence by simply replacing the original transmission line with a less faulty one. Unfortunately, this condition also limits the possible distance between the communicating parties, Alice and Bob, to a few hundred kilometers. To overcome this problem, we design a QKD protocol which allows Alice and Bob to distinguish system errors from eavesdropping errors. If they are able to identify the origin of their errors, they can detect eavesdropping even when the system error rate exceeds the eavesdropping error rate. To achieve this, the proposed protocol employs an alternative encoding of information in two-dimensional photon states. Errors manifest themselves as quantum bit and as index transmission errors with a distinct correlation between them in case of intercept-resend eavesdropping. As a result, Alice and Bob can tolerate lower eavesdropping and higher system error rates without compromising their privacy.

Frontiers in Photonics

The classical free-space solutions of Maxwell’s equations for light propagation in one dimension ... more The classical free-space solutions of Maxwell’s equations for light propagation in one dimension include wave packets of any shape that travel at the speed of light. This includes highly-localised wave packets that remain localised at all times. Motivated by this observation, this paper builds on recent work by Southall et al. [J. Mod. Opt. 68, 647 (2021)] and shows that a local description of the quantised electromagnetic field, which supports such solutions and which must overcome several no-go theorems, is indeed possible. Starting from the assumption that the basic building blocks of photonic wave packets are so-called bosons localised in position (blips), we identify the relevant Schrödinger equation and construct Lorentz-covariant electric and magnetic field observables. In addition we show that our approach simplifies to the standard description of quantum electrodynamics when restricted to a subspace of states.

Symmetry

In recent years, non-Hermitian quantum physics has gained a great deal of popularity in the quant... more In recent years, non-Hermitian quantum physics has gained a great deal of popularity in the quantum optics and condensed matter communities in order to model quantum systems with varying symmetries. In this paper, we identify a non-standard inner product that implies bosonic commutator relations for local electric and magnetic field observables and leads to a natural local biorthogonal description of the quantised electromagnetic field. When comparing this description with an alternative local Hermitian description, in which the states of local photonic particles, i.e., of so-called bosons localised in position (blips), are orthogonal under the conventional Hermitian inner product, we find that there is an equivalence between the two approaches. Careful consideration needs to be given to the physical interpretation of the different descriptions. Whether a Hermitian or a non-Hermitian approach is more suitable depends on the circumstances that we want to model.

Frontiers in Physics

In this review we present the problem of time in quantum physics, including a short history of th... more In this review we present the problem of time in quantum physics, including a short history of the problem and the known objections about considering time as a quantum observable. The need to deal with time as an observable is elaborated through some unresolved problems. The lack of a consistent theory of time is currently hindering the formulation of a full-fledged theory of quantum gravity. It is argued that the proposal set forth by several authors of considering an intrinsic measurement of quantum time, besides having the conventional external time, is compelling. Recently several suggestions have been put forward to revive the proposal of Page and Wootters (1983), elaborating and resolving some of the main ambiguities of the original proposal and opening new scope for understanding its content. The approach followed in these new contributions exposes the need to go beyond the limitations enforced by the conventional approach of quantum physics. The attitude of covariant loop qu...

The Casimir effect, which predicts the emergence of an attractive force between two parallel, hig... more The Casimir effect, which predicts the emergence of an attractive force between two parallel, highly reflecting plates in vacuum, plays a vital role in various fields of physics, from quantum field theory and cosmology to nanophotonics and condensed matter physics. Nevertheless, Casimir forces still lack an intuitive explanation and current derivations rely on regularisation procedures to remove infinities. Starting from special relativity and treating space and time coordinates equivalently, this paper overcomes no-go theorems of quantum electrodynamics and obtains a local relativistic quantum description of the electromagnetic field in free space. When extended to cavities, our approach can be used to calculate Casimir forces directly in position space without the introduction of cut-off frequencies.

arXiv: Quantum Physics, 2016

Open quantum systems usually reach a unique stationary state with ergodic dynamics. In other word... more Open quantum systems usually reach a unique stationary state with ergodic dynamics. In other words, the ensemble averages and the time averages of the expectation values of open quantum systems are usually the same for all quantum trajectories. Although open quantum systems are in general ergodic, many classical stochastic processes are not. Hence if classical physics emerges from microscopic quantum models, there have to be mechanisms which induce non-ergodicity in open quantum systems. In this paper, we identify such a mechanism by showing that quantum feedback dramatically alters the dynamics of open quantum systems, thereby possibly inducing non-ergodicity and a persistent dependence of ensemble averages on initial conditions. As a concrete example, we study an optical cavity inside an instantaneous quantum feedback loop.

EPL (Europhysics Letters), 2020

It is well known that quantum feedback can alter the dynamics of open quantum systems dramaticall... more It is well known that quantum feedback can alter the dynamics of open quantum systems dramatically. In this paper, we show that non-ergodicity may be induced through quantum feedback and resultantly create system dynamics that have lasting dependence on initial conditions. To demonstrate this, we consider an optical cavity inside an instantaneous quantum feedback loop, which can be implemented relatively easily in the laboratory. Non-ergodic quantum systems are of interest for applications in quantum information processing, quantum metrology and quantum sensing and could potentially aid the design of thermal machines whose efficiency is not limited by the laws of classical thermodynamics.

Journal of Modern Optics, 2018

Journal of Modern Optics, 2017

There are many ways to decompose the Hilbert space H of a composite quantum system into tensor pr... more There are many ways to decompose the Hilbert space H of a composite quantum system into tensor product subspaces. Different subsystem decompositions generally imply different interaction Hamiltonians V , and therefore different expectation values for subsystem observables. This means that the uniqueness of physical predictions is not guaranteed, despite the uniqueness of the total Hamiltonian H and the total Hilbert space H. Here we use Clausius' version of the second law of thermodynamics (CSL) and standard identifications of thermodynamic quantities to identify possible subsystem decompositions. It is shown that agreement with the CSL is obtained, whenever the total Hamiltonian and the subsystem-dependent interaction Hamiltonian commute (i.e. [H, V ] = 0). Not imposing this constraint can result in the transfer of heat from a cooler to a hotter subsystem, in conflict with thermodynamics. We also investigate the status of the CSL with respect to non-standard definitions of thermodynamic quantities and quantum subsystems.

Nature Photonics, 2016

A double-slit experiment performed with two rubidium atoms precisely held in an optical lattice i... more A double-slit experiment performed with two rubidium atoms precisely held in an optical lattice inside an optical cavity provides a new platform for exploring quantum effects.

Acta Physica Polonica A, 2002

ISCS 2014: Interdisciplinary Symposium on Complex Systems, 2015

arXiv (Cornell University), Jul 30, 2012

arXiv (Cornell University), Jun 15, 2010

arXiv (Cornell University), Jun 15, 2010

Cavity-mediated cooling has the potential to become one of the most efficient techniques to cool ... more Cavity-mediated cooling has the potential to become one of the most efficient techniques to cool molecular species down to very low temperatures. In this paper we analyse cavity cooling with single-laser driving for relatively large cavity decay rates kappa\kappakappa and relatively large phonon frequencies nu and show that it is essentially the same as ordinary laser cooling. This is done by calculating the stationary state phonon number mrmssm^{\rm ss}mrmss and the cooling rate gamma\gammagamma as a function of the system parameters. For example, when nu is either much larger or much smaller than kappa, the minimum stationary state phonon number scales as kappa^2/16nu^2 (strong confinement regime) and as kappa/4nu (weak confinement regime), respectively.

Nature Photonics, Apr 28, 2016

A double-slit experiment performed with two rubidium atoms precisely held in an optical lattice i... more A double-slit experiment performed with two rubidium atoms precisely held in an optical lattice inside an optical cavity provides a new platform for exploring quantum effects.

EPL, Jun 30, 2020

It is well known that quantum feedback can alter the dynamics of open quantum systems dramaticall... more It is well known that quantum feedback can alter the dynamics of open quantum systems dramatically. In this paper, we show that non-Ergodicity may be induced through quantum feedback and resultantly create system dynamics that have lasting dependence on initial conditions. To demonstrate this, we consider an optical cavity inside an instantaneous quantum feedback loop, which can be implemented relatively easily in the laboratory. Non-Ergodic quantum systems are of interest for applications in quantum information processing, quantum metrology and quantum sensing and could potentially aid the design of thermal machines whose efficiency is not limited by the laws of classical thermodynamics.

Sensors

One way of optically monitoring molecule concentrations is to utilise the high sensitivity of the... more One way of optically monitoring molecule concentrations is to utilise the high sensitivity of the transmission and reflection rates of Fabry-Pérot cavities to changes of their optical properties. Up to now, intrinsic and extrinsic Fabry-Pérot cavity sensors have been considered with analytes either being placed inside the resonator or coupled to evanescent fields on the outside. Here we demonstrate that Fabry-Pérot cavities can also be used to monitor molecule concentrations non-invasively and remotely, since the reflection of light from the target molecules back into the Fabry-Pérot cavity adds upwards peaks to the minima of its overall reflection rate. Detecting the amplitude of these peaks reveals information about molecule concentrations. By using an array of optical cavities, a wide range of frequencies can be probed at once and a unique optical fingerprint can be obtained.

arXiv (Cornell University), Aug 10, 2022

One way of optically monitoring molecule concentrations is to utilise the high sensitivity of the... more One way of optically monitoring molecule concentrations is to utilise the high sensitivity of the transmission and reflection rates of Fabry-Pérot cavities to changes of their optical properties. Up to now, intrinsic and extrinsic Fabry-Pérot cavity sensors have been considered with analytes either being placed inside the resonator or coupled to evanescent fields on the outside. Here we show that Fabry-Pérot cavities can also be used to monitor molecule concentrations non-invasively and remotely, since the reflection of light from the target molecules back into the Fabry-Pérot cavity adds upwards peaks to the minima of its overall reflection rate. Detecting the amplitude of these peaks reveals information about molecule concentrations. By using an array of optical cavities, a wide range of frequencies can be probed at once and a unique optical fingerprint can be obtained.

arXiv (Cornell University), Dec 5, 2011

Employing the fundamental laws of quantum physics, Quantum Key Distribution (QKD) promises the un... more Employing the fundamental laws of quantum physics, Quantum Key Distribution (QKD) promises the unconditionally secure distribution of cryptographic keys. However, in practical realisations, a QKD protocol is only secure, when the quantum bit error rate introduced by an eavesdropper unavoidably exceeds the system error rate. This condition guarantees that an eavesdropper cannot disguise his presence by simply replacing the original transmission line with a less faulty one. Unfortunately, this condition also limits the possible distance between the communicating parties, Alice and Bob, to a few hundred kilometers. To overcome this problem, we design a QKD protocol which allows Alice and Bob to distinguish system errors from eavesdropping errors. If they are able to identify the origin of their errors, they can detect eavesdropping even when the system error rate exceeds the eavesdropping error rate. To achieve this, the proposed protocol employs an alternative encoding of information in two-dimensional photon states. Errors manifest themselves as quantum bit and as index transmission errors with a distinct correlation between them in case of intercept-resend eavesdropping. As a result, Alice and Bob can tolerate lower eavesdropping and higher system error rates without compromising their privacy.

Frontiers in Photonics

The classical free-space solutions of Maxwell’s equations for light propagation in one dimension ... more The classical free-space solutions of Maxwell’s equations for light propagation in one dimension include wave packets of any shape that travel at the speed of light. This includes highly-localised wave packets that remain localised at all times. Motivated by this observation, this paper builds on recent work by Southall et al. [J. Mod. Opt. 68, 647 (2021)] and shows that a local description of the quantised electromagnetic field, which supports such solutions and which must overcome several no-go theorems, is indeed possible. Starting from the assumption that the basic building blocks of photonic wave packets are so-called bosons localised in position (blips), we identify the relevant Schrödinger equation and construct Lorentz-covariant electric and magnetic field observables. In addition we show that our approach simplifies to the standard description of quantum electrodynamics when restricted to a subspace of states.

Symmetry

In recent years, non-Hermitian quantum physics has gained a great deal of popularity in the quant... more In recent years, non-Hermitian quantum physics has gained a great deal of popularity in the quantum optics and condensed matter communities in order to model quantum systems with varying symmetries. In this paper, we identify a non-standard inner product that implies bosonic commutator relations for local electric and magnetic field observables and leads to a natural local biorthogonal description of the quantised electromagnetic field. When comparing this description with an alternative local Hermitian description, in which the states of local photonic particles, i.e., of so-called bosons localised in position (blips), are orthogonal under the conventional Hermitian inner product, we find that there is an equivalence between the two approaches. Careful consideration needs to be given to the physical interpretation of the different descriptions. Whether a Hermitian or a non-Hermitian approach is more suitable depends on the circumstances that we want to model.

Frontiers in Physics

In this review we present the problem of time in quantum physics, including a short history of th... more In this review we present the problem of time in quantum physics, including a short history of the problem and the known objections about considering time as a quantum observable. The need to deal with time as an observable is elaborated through some unresolved problems. The lack of a consistent theory of time is currently hindering the formulation of a full-fledged theory of quantum gravity. It is argued that the proposal set forth by several authors of considering an intrinsic measurement of quantum time, besides having the conventional external time, is compelling. Recently several suggestions have been put forward to revive the proposal of Page and Wootters (1983), elaborating and resolving some of the main ambiguities of the original proposal and opening new scope for understanding its content. The approach followed in these new contributions exposes the need to go beyond the limitations enforced by the conventional approach of quantum physics. The attitude of covariant loop qu...

The Casimir effect, which predicts the emergence of an attractive force between two parallel, hig... more The Casimir effect, which predicts the emergence of an attractive force between two parallel, highly reflecting plates in vacuum, plays a vital role in various fields of physics, from quantum field theory and cosmology to nanophotonics and condensed matter physics. Nevertheless, Casimir forces still lack an intuitive explanation and current derivations rely on regularisation procedures to remove infinities. Starting from special relativity and treating space and time coordinates equivalently, this paper overcomes no-go theorems of quantum electrodynamics and obtains a local relativistic quantum description of the electromagnetic field in free space. When extended to cavities, our approach can be used to calculate Casimir forces directly in position space without the introduction of cut-off frequencies.

arXiv: Quantum Physics, 2016

Open quantum systems usually reach a unique stationary state with ergodic dynamics. In other word... more Open quantum systems usually reach a unique stationary state with ergodic dynamics. In other words, the ensemble averages and the time averages of the expectation values of open quantum systems are usually the same for all quantum trajectories. Although open quantum systems are in general ergodic, many classical stochastic processes are not. Hence if classical physics emerges from microscopic quantum models, there have to be mechanisms which induce non-ergodicity in open quantum systems. In this paper, we identify such a mechanism by showing that quantum feedback dramatically alters the dynamics of open quantum systems, thereby possibly inducing non-ergodicity and a persistent dependence of ensemble averages on initial conditions. As a concrete example, we study an optical cavity inside an instantaneous quantum feedback loop.

EPL (Europhysics Letters), 2020

It is well known that quantum feedback can alter the dynamics of open quantum systems dramaticall... more It is well known that quantum feedback can alter the dynamics of open quantum systems dramatically. In this paper, we show that non-ergodicity may be induced through quantum feedback and resultantly create system dynamics that have lasting dependence on initial conditions. To demonstrate this, we consider an optical cavity inside an instantaneous quantum feedback loop, which can be implemented relatively easily in the laboratory. Non-ergodic quantum systems are of interest for applications in quantum information processing, quantum metrology and quantum sensing and could potentially aid the design of thermal machines whose efficiency is not limited by the laws of classical thermodynamics.

Journal of Modern Optics, 2018

Journal of Modern Optics, 2017

There are many ways to decompose the Hilbert space H of a composite quantum system into tensor pr... more There are many ways to decompose the Hilbert space H of a composite quantum system into tensor product subspaces. Different subsystem decompositions generally imply different interaction Hamiltonians V , and therefore different expectation values for subsystem observables. This means that the uniqueness of physical predictions is not guaranteed, despite the uniqueness of the total Hamiltonian H and the total Hilbert space H. Here we use Clausius' version of the second law of thermodynamics (CSL) and standard identifications of thermodynamic quantities to identify possible subsystem decompositions. It is shown that agreement with the CSL is obtained, whenever the total Hamiltonian and the subsystem-dependent interaction Hamiltonian commute (i.e. [H, V ] = 0). Not imposing this constraint can result in the transfer of heat from a cooler to a hotter subsystem, in conflict with thermodynamics. We also investigate the status of the CSL with respect to non-standard definitions of thermodynamic quantities and quantum subsystems.

Nature Photonics, 2016

A double-slit experiment performed with two rubidium atoms precisely held in an optical lattice i... more A double-slit experiment performed with two rubidium atoms precisely held in an optical lattice inside an optical cavity provides a new platform for exploring quantum effects.

Acta Physica Polonica A, 2002

ISCS 2014: Interdisciplinary Symposium on Complex Systems, 2015

Employing the fundamental laws of quantum physics, Quantum Key Distribution (QKD) achieves the un... more Employing the fundamental laws of quantum physics, Quantum Key Distribution (QKD) achieves the unconditionally secure distribution of cryptographic keys. Its security arises from the fact that an eavesdropper unavoidably introduces the so-called quantum bit errors. If these errors exceed system errors, his presence can be detected and the key transmission can be aborted. Otherwise, an eavesdropper could disguise his presence as system errors after replacing some of the equipments of the communicating parties. This condition for the security of QKD protocols limits the possible communication distance in practical implementations. In this paper, we propose to significantly increase the communication distance of QKD by using protocols with not only one but two different types of eavesdropping errors, such that eavesdropping and system errors do not affect the communication in different ways. This makes it possible to detect eavesdropping, even when the system errors exceed the eavesdropping errors. In order to illustrate this, we analyse the KMB09 protocol [Khan et al., New J Phys. 11 2009 063043] with only two-dimensional photon states and calculate the Quantum Bit Error Rate (QBER), the Index Transmission Error-Rate (ITER) and the efficiencies with and without eavesdropping of this protocol.