Search Talks

The anti-de Sitter (AdS) space is of great interest in contemporary
theoretical physics due to the AdS/CFT correspondence. However, the
question of stability of AdS space is unanswered till now. After
giving the motivation for studies of asymptotically AdS spaces, I will
review dynamics of such spacetimes in the context of AdS instability
problem. This survey will include: evidence for instability of AdS
space, existence and properties of time-periodic solutions, and
finally an application of analytical technique called multiscale or
resonant approximation approach. If time permits, I will comment on
other asymptotically AdS solutions. Along with the results, I will
highlight some details of methods relevant to the topic.

How does thermalization in quantum systems work? Naively, the unitary time evolution prevents thermalization, but one can easily show that in general quantum systems thermalize when brought into contact with a thermal bath. In noninteracting systems, the approach to the thermal value can be either ballistic or diffusive depending on particle statistics and bath temperature.

However, many systems cannot be thermalized when placed in a bath: glasses.

I will discuss a disorderfree model of an organic electronic glass that is formed through rapid supercooling. Geometric frustration and long-range interactions cause the Arrhenius-type freezing.

Quenched disorder can also lead to glassiness, a phenomenon known as many-body localization. In this case, thermalization is prevented by the existence of extensively many local integrals of motion. I will show how to compute these integrals of motion and their properties.

I will argue that the standard model contains a rather strong hint that -- instead of being simply an ordinary continuous 4D manifold -- spacetime is actually the product of a 4D manifold and a certain discrete/finite 6D space (i.e. there are 6D discrete/finite "extra dimensions").  I will introduce this idea and the evidence for it in simple way, and then discuss various outstanding puzzles and future directions.

I will discuss the coupling of non-relativistic field theories to curved spacetime, and develop a framework for analyzing the possible structure of non-relativistic (Lifshitz) scale anomalies using a cohomological formulation of the Wess-Zumino consistency condition. I will compare between cases with or without Galilean boost symmetry, and between cases with or without an equal time foliation of spacetime. In 2+1 dimensions with a dynamical critical exponent of z=2, the absence of a foliation structure allows for an A-type anomaly in the Galilean case, but also introduces the possibility of an infinite set of B-type anomalies.

I will also derive Ward identities for flat space correlation functions in Lifshitz field theories, and develop a method for calculating Lifshitz anomaly coefficients from these correlation functions using split dimensional regularization.

The on-demand generation of bright entangled photon pairs is highly needed in quantum optics and emerging quantum information applications. However, a quantum light source combining both high fidelity and on-demand bright emission has proven elusive with current leading photon technologies. In this work we present a new bright nanoscale source of strongly entangled photon pairs generated with a position controlled nanowire quantum dot. The major breakthrough in the nanowire growth to achieve both bright photon emission and highly entangled photon pairs will be discussed [2, 3]. Recent experiments show the entanglement fidelity approaching unity, while enhancing the photon pair efficiency beyond state-of-the-art. We further demonstrate violation of the famous Clauser-Horne-Shimony-Holt inequality in the traditional linear basis [4]. This is the first bright nanoscale source of entangled photon pairs capable of violating Bell`s inequalities, opening up future experiments in quantum optics and developments in quantum information applications.

For long-distance quantum communication we convert polarization entangled photons generated by a single quantum dot into time-bin entangled photons by sending them through a polarization-time-bin interface [5]. Importantly, this conversion is performed without loss of entanglement strength. Time-bin entanglement is more robust for long-distance quantum communication than polarization entanglement, since time-bin entangled photons are insensitive to thermal and mechanical disturbances in optical fibers.

References

[1]      M. A. M. Versteegh, M. E Reimer, K. D Jöns, D. Dalacu, P. J. Poole, A. Gulinatti, A. Giudice, and V. Zwiller, Nature Commun. 5, 5298 (2014).

[2]      D. Dalacu, K. Mnaymneh, J. Lapointe, X. Wu, P. J. Poole, G. Bulgarini, V. Zwiller, and M. E. Reimer, Nano Lett. 12 (11), 5919-5923 (2012).

[3]      M. E. Reimer et al., Phys. Rev. B 93, 195316 (2016).

[4]      K. D. Jöns et al., arXiv:1510.03897 (2015).

[5]      M. A. M. Versteegh, M. E. Reimer, A. A. van den Berg, G. Juska, V. Dimastrodonato, A. Gocalinska, E. Pelucchi, and V. Zwiller, Phys. Rev. A 92, 033802 (2015).

Two-dimensional materials such as graphene sheets can serve as excellent detectors for dark matter (DM) with couplings to electrons. The ionization energy of graphene is O(eV), making it sensitive to DM as light as an MeV, and the ejected electron may be detected without rescattering in the target, preserving directional information. I will describe the first experimental proposal for directional detection of MeV-GeV scale DM, which can be implemented in the PTOLEMY relic neutrino experiment and has comparable sensitivity to proposals using semiconductor targets. I will also describe some potential avenues for using gapless systems like Weyl semimetals to detect DM down to the keV limit for warm DM.