Active Interferometry with Gaussian Channels

We consider an interferometer that contains active elements, such as a parametric amplifier, with general two-mode Gaussian unitary channels rather than the usually considered phase-shift channel. We concentrate on a scheme based on the recently proposed pumped-up SU(1,1) active interferometer where all input particles participate in the parameter estimation, and from which a conventional SU(1,1) interferometer is a limiting case. Using the covariance matrix formalism, we derive the quantum Fisher information of this active interferometer with a general two-mode Gaussian unitary channel, as well as the sensitivity for a number-sum measurement scheme, finding simple expressions for the latter. As an example application, we apply our results to Bose-Einstein condensates (BECs), and in particular a BEC gravitational-wave detector based on resonance, finding that the sensitivity of the detector can be improved by several orders of magnitude with this new interferometry scheme.Comment: 17 pages, 1 figur

Comment on "Interaction of a Bose-Einstein condensate with a gravitational wave"

A gravitational-wave (GW) detector that utilizes the phononic excitations of a Bose-Einstein condensate (BEC) has recently been proposed [NJP 16, 085003 (2014)]. A subsequent and independent study, [arXiv:1807.07046v1], has suggested an alternative GW detection scheme that also uses phonons of a BEC but which was found to be many orders of magnitude away from being feasible. Here we make clear that the two proposed schemes are very different and that the conclusions of [arXiv:1807.07046v1] do not apply to the original proposal [NJP 16, 085003 (2014)].Comment: 3 page

Quantum simulation of dark energy candidates

Additional scalar fields from scalar-tensor, modified gravity or higher dimensional theories beyond general relativity may account for dark energy and the accelerating expansion of the Universe. These theories have lead to proposed models of screening mechanisms, such as chameleon and symmetron fields, to account for the tight experimental bounds on fifth-force searches. Cold atom systems have been very successfully used to constrain the parameters of these screening models, and may in future eliminate the interesting parameter space of some models entirely. In this paper, we show how to manipulate a Bose-Einstein condensate to simulate the effect of any screened scalar field model coupled conformally to the metric. We give explicit expressions for the simulation of various common models. This result may be useful for investigating the computationally challenging evolution of particles on a screened scalar field background, as well as for testing the metrology scheme of an upcoming detector proposal.Comment: 26 pages, 3 figure

E6 inspired supersymmetric models

This work investigates extensions to the Standard Model that are inspired by supersymmetric models with an E6 gauge group. The models are non-minimal supersymmetric theories which keep the Higgs mass stable against the quantum corrections from higher energy physics, but do not contain the mu-problem or little hierarchy problem of the Minimal Supersymmetric Standard Model (MSSM). Also, unlike conventional Grand Unified Theories, the E6 inspired models do not contain any doublet-triplet splitting and the Minimal E6 Supersymmetric Model (ME6SSM) only contains complete E6 multiplets at low energies. A particularly exciting feature of the ME6SSM is the prediction of gauge coupling unification at the Planck scale rather than the conventional GUT scale, hinting at a potential unification of the Standard Model forces with quantum gravity.If extended with a discrete non-Abelian family symmetry, the E6 inspired models can explain the masses and mixings of the quarks and leptons that are observed in particle experiments. These are not understood in the Standard Model since they are free parameters, creating a flavour problem for the theory. Extending the Standard Model or MSSM with a family symmetry offers an attractive resolution to the flavour problem, and the recent discovery of neutrino oscillations, which indicate a high-level of symmetry in the lepton mixings, has led to a renewed interest in these models. However, explaining why the Higgs mass is small is essential in these models since it sets the scale for the quark and lepton masses. This motivates the synthesis of a family symmetry with the E6 inspired supersymmetric models, which resolves a number of problems facing the Standard Model including the hierarchy problem and the favour problem. A particular success of the resulting models is their ability to suppress proton decay and favour changing neutral currents, from supersymmetry and extended Higgs sectors, using the same family symmetry that is responsible for a tri-bi-maximal mixing of leptons

Gravitationally-induced entanglement in cold atoms

A promising route to testing quantum gravity in the laboratory is to look for gravitationally-induced entanglement (GIE) between two or more quantum matter systems. Proposals for such tests have principally used microsolid systems, with highly non-classical states, such as N00N states or highly-squeezed states. Here, we consider, for the first time, GIE between two atomic gas interferometers as a test of quantum gravity. We propose placing the two interferometers next to each other in parallel and looking for correlations in the number of atoms at the output ports as evidence of GIE and quantum gravity. GIE is possible without challenging macroscopic superposition states, such as N00N or Schr\"odinger cat states, and instead there can be just classical-like 'coherent' states of atoms. This requires the total mass of the atom interferometers to be on the Planck mass scale, and long integration times. However, with current state-of-the-art quantum squeezing in cold atoms, we argue that the mass scale can be reduced to approachable levels and detail how such a mass scale can be achieved in the near future.Comment: 14 pages, 3 figure

Exploring the unification of quantum theory and general relativity with a Bose-Einstein condensate

Despite almost a century's worth of study, it is still unclear how general relativity (GR) and quantum theory (QT) should be unified into a consistent theory. The conventional approach is to retain the foundational principles of QT, such as the superposition principle, and modify GR. This is referred to as `quantizing gravity', resulting in a theory of `quantum gravity'. The opposite approach is `gravitizing QT' where we attempt to keep the principles of GR, such as the equivalence principle, and consider how this leads to modifications of QT. What we are most lacking in understanding which route to take, if either, is experimental guidance. Here we consider using a Bose-Einstein condensate (BEC) to search for clues. In particular, we study how a single BEC in a superposition of two locations could test a gravitizing QT proposal where wavefunction collapse emerges from a unified theory as an objective process, resolving the measurement problem of QT. Such a modification to QT due to general relativistic principles is testable near the Planck mass scale, which is much closer to experiments than the Planck length scale where quantum, general relativistic effects are traditionally anticipated in quantum gravity theories. Furthermore, experimental tests of this proposal should be simpler to perform than recently suggested experiments that would test the quantizing gravity approach in the Newtonian gravity limit by searching for entanglement between two massive systems that are both in a superposition of two locations.Comment: 51 pages, 10 figure

Quantum-enhanced screened dark energy detection

We propose an experiment based on a Bose-Einstein condensate interferometer for strongly constraining fifth-force models. Additional scalar fields from modified gravity or higher dimensional theories may account for dark energy and the accelerating expansion of the Universe. These theories have led to proposed screening mechanisms to fit within the tight experimental bounds on fifth-force searches. We show that our proposed experiment would greatly improve the existing constraints on these screening models by many orders of magnitude, entirely eliminating the remaining parameter space of the simplest of these models.Comment: 20 pages, 6 figure

Quantum-enhanced screened dark energy detection

We propose an experiment based on a Bose–Einstein condensate interferometer for strongly constraining fifth-force models. Additional scalar fields from modified gravity or higher dimensional theories may account for dark energy and the accelerating expansion of the Universe. These theories have led to proposed screening mechanisms to fit within the tight experimental bounds on fifth-force searches. We show that our proposed experiment would greatly improve the existing constraints on these screening models by many orders of magnitude

Quantum Gravity Signature in a Thermodynamic Observable

Proposed experiments for obtaining empirical evidence for a quantum description of gravity in a table-top setting focus on detecting quantum information signatures, such as entanglement or non-Gaussianity production, in gravitationally interacting quantum systems. Here, we explore an alternative approach where the quantization of gravity could be inferred through measurements of macroscopic, thermodynamical quantities, without the need for addressability of individual quantum systems. To demonstrate the idea, we take as a case study a gravitationally self-interacting Bose gas, and consider its heat capacity. We find a clear-cut distinction between the predictions of a classical gravitational interaction and a quantum gravitational interaction in the heat capacity of the Bose gas