AMQP Seminar Series

A series of talks by visitors to the AMQP Group, Department of Physics, Swansea University.


If you would like to schedule a talk, or have any queries, please contact James Bateman


If you would like to schedule a talk, or have any queries, please contact James Bateman

Upcoming talks

Carrie Ann Weidner (Institut for Fysik og Astronomi, Aarhus Universitet)

Wed 10. April 2019 at 14:00

Playing quantum games with ultracold atoms

The first demonstrations of quantum gas microscopes [1,2] in 2009-10 opened up a new avenue for research in quantum simulation in few- and many-body systems. The quantum gas microscope being developed at Aarhus University combines traditional microscopy with control over the atoms' internal state [3] and the potential they experience, while also being capable of performing non-destructive measurements of the atomic density (e.g. for measurement of magnetic fields [4]). Our system has also been used to demonstrate remote optimization of experimental parameters by experts and citizen scientists [5].

In this talk, I will describe our experimental setup and outline our plans for the future, including further exploration of remote optimization in the context of spintronics. I will also highlight some of the other "quantum-based" tools developed by the group for research [6], citizen science [7], and didactic [8] purposes.

[1] W. Bakr et al, Nature 462, 74, (2009). [2] J.F. Sherson et al, Nature 467, 68, (2010). [3] C. Weitenberg et al, Nature 471, 319, (2011). [4] O. Elíasson et al, J. Phys. B. 52, 7, (2019). [5] R. Heck et al. PNAS 115, 48, (2018). [6] J.J.W.H. Sørensen et al. Phys. Rev A. 98, 022119, (2018). [7] [8] J.J.W.H. Sørensen et al, arXiv:1807.11731v2, (2018). (see also

Previous talks

Prof. Guido Pupillo (Strasbourg)

Tue 26. March 2019 at 13:00

Exciton and charge transport via cavity-mediated long-range interactions

Strong light-matter interactions are playing an increasingly crucial role in the understanding and engineering of new states of matter with relevance to the fields of quantum optics, solid state physics and material science. Recent experiments with molecular semiconductors have shown that charge conductivity can be dramatically enhanced by coupling intra-molecular electronic transitions to the bosonic field of a cavity or of a plasmonic structure prepared in its vacuum state, even at room temperature [1]. In this talk, we discuss a proof-of-principle model for charge and exciton transport where light-matter hybridization enabled by long-range cavity mediated interactions provides an enhancement of conductivity in the steady-state. We discuss the roles of disorder and finite electronic band-width in the light-matter dressing and current enhancement. We demonstrate that under certain experimentally relevant conditions this enhancement can reach orders of magnitude [2,3]. We conclude with a discussion of open questions in the field of vacuum-induced quantum materials.


  1. E. Orgiu et al., Nature Materials 14, 1123 (2015)
  2. D. Hagenmuller, J. Schachenmayer, S. Schutz, C. Genes, and G. Pupillo, Phys. Rev. Lett. 119, 223601 (2107)
  3. D. Hagenmuller, S. Schutz, J. Schachenmayer, C. Genes, and G. Pupillo, Phys. Rev. B 97, 205303 (2018)

Dr Enrique Rico (University of the Basque Country)

Wed 27. February 2019 at 14:00

SO(3) “Nuclear Physics” with ultracold Gases

An ab initio calculation of nuclear physics from Quantum Chromodynamics (QCD), the fundamental SU(3) gauge theory of the strong interaction, remains an outstanding challenge. Here, we discuss the emergence of key elements of nuclear physics using an SO(3) lattice gauge theory as a toy model for QCD. We show that this model is accessible to state-of-the-art quantum simulation experiments with ultracold atoms in an optical lattice. First, we demonstrate that our model shares characteristic many-body features with QCD, such as the spontaneous breakdown of chiral symmetry, its restoration at finite baryon density, as well as the existence of few-body bound states. Then we show that in the one-dimensional case, the dynamics in the gauge invariant sector can be encoded as a spin s=3/2 Heisenberg model, i.e., as quantum magnetism, which has a natural realisation with bosonic mixtures in optical lattices, and thus sheds light on the connection between non-Abelian gauge theories and quantum magnetism.

Reference: Annals of Physics, vol. 393, pp. 466-483 (2018)

Glenn Jones (Swansea (Geophysics))

Wed 13. February 2019 at 14:00

Seismic investigation of the crustal structure beneath the Greenland Ice Sheet

Since the early 1990’s climatic forcing has significantly accelerated the mass loss of the Greenland Ice Sheet (GrIS), which has contributed ~10% of mean global sea level rise. Basal slip is the dominant mechanism by which glaciers and ice-sheets flow. It is a major source of uncertainty in simulations of mass loss from the GrIS and its contribution to sea level rise. Subsurface geology has been identified as a strong control on the basal slip and ice flow velocity, but to date, has received relatively little attention in Greenland.

Seismic methods are the tools of choice in probing the internal structure of the Earth. Surface Rayleigh waves are the seismic wave of choice in understanding the upper crust of the Earth but like all waveform based methods resolution is frequency dependent. Typically, seismic methods rely on earthquake data, whose periods are too large to image any potential sedimentary rock beneath an ice sheet. However, recent advances in the use of the Earth's ambient noise and the availability of large continuous seismic datasets have allowed for higher frequency data to be extracted leading to unprecedented resolution images. We extract high frequency ocean generated Rayleigh waves using a time-frequency representation of their polarization properties. Using the ratio of the horizontal to vertical ratio of displacement of these Rayleigh waves we invert for 1D structure of the subsurface using a Monte-Carlo based optimization methodology. I present here passive seismic observations and discuss the implications of understanding the subglacial geology and the impacts passive seismic methodologies can make in other fields.

Dr Piero Naldesi (LPMMC, Grenoble-Alpes University)

Tue 29. January 2019 at 14:00

Angular momentum fractionalization: the quantum advantage of entangled bosons

Quantum mechanics is characterized by quantum coherence and entanglement. After having discovered how these fundamental concepts govern the physical reality, scientists have been devoting intense efforts to harness them to shape the future science and technology[1]. This is a highly non trivial task because most often quantum coherence and entanglement are difficult to access[2]. Here, we present a quantum manybody system in which quantum coherence and entanglement directly imply the quantum advantage of quantum technology over the classical one. Our physical system is made of strongly correlated attracting neutral bosons flowing in a ringshaped potential of mesoscopic size. Quantum analogs of bright solitons are formed in the system by the attractive interactions, and, as a genuine quantum-many-body feature, we demonstrate that an angular momentum fractionalization occurs. As a consequence, the matter-wave current in our system is able to react to very small changes of rotation or other artificial gauge fields. We discuss how our results put the basis to devise rotation sensors and gyroscopes with enhanced sensitivity.

[1] J. P. Dowling and G. J. Milburn, Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 361, 1655 (2003).

[2] A. Acin, I. Bloch, H. Buhrman, T. Calarco, C. Eichler, J. Eisert, D. Esteve, N. Gisin, S. J. Glaser, F. Jelezko, et al., New Journal of Physics 20, 080201 (2018).

[3] R. Kanamoto, H. Saito, and M. Ueda, Physical Review Letters 94, 090404 (2005).

[4] P. Calabrese and J.-S. Caux, Physical Review Letters 98, 150403 (2007).

[5] P. Naldesi, J. Polo Gomez, A. Minguzzi, B. Malomed, M. Olshanii, and L. Amico, ArXiv e-prints , arXiv:1804.10133 (2018), arXiv:1804.10133 [condmat.quant-gas].

George Winstone (Northwestern University)

Wed 09. January 2019 at 14:00

Nonlinear optomechanical sensing and gravitational wave detection

We discuss nonlinear sensing modes in the context of optically levitated nanoparticles, specifically for the cases of detecting surface forces and electric fields. We also give a brief overview of near future plans looking towards detecting gravitational waves in a room scale optomechanical setup.

Earl Campbell (Sheffield)

Wed 19. December 2018 at 14:00



Steve Brierley (Riverlane)

Thu 29. November 2018 at 14:00

Quantum Simulation on a Quantum Computer

Computers are central to the design of many new products: modelling the airflow over a wing, simulating the mechanics of an engine, laying out complex electronic circuits. But when we try to simulate systems at the level of individual atoms, the physical laws that govern their behaviour are fundamentally different – they are quantum in nature. Even huge supercomputers are limited to approximations of what is really happening. As a result, the design of new drugs and materials remains primarily a laboratory rather than a computational exercise. Quantum computers offer a solution to this problem leading to huge savings in R&D costs and new advances in our understanding of physics. I will review recent advances in quantum computing and in particular quantum algorithms for simulation.

Simon L. Cornish (Joint Quantum Centre, Durham University)

Wed 21. November 2018 at 14:00

Building a quantum simulator using ultracold molecules: rotational coherences in optically trapped RbCs

Polar molecules offer a new platform for the simulation of many-body quantum systems with long-range interactions, utilizing the electrostatic interaction between their electric dipole moments and the rich internal structure associated with the molecular rotation. Realizing long-lived, trapped samples of molecules with full quantum control of the molecular internal state is an essential first step towards building such a quantum simulator.

In this talk I will explain how we create ultracold gases of RbCs molecules from a mixed species atomic gas using magnetoassociation on a Feshbach resonance followed by optical transfer using stimulated Raman adiabatic passage. We then use precision microwave spectroscopy of the rotational transition to probe the rich hyperfine structure of the molecule and exploit coherent Rabi oscillations to transfer the total population of molecules between hyperfine levels. We subsequently investigate the AC Stark effect due to the trapping light in low-lying rotational levels and reveal a rich energy structure with many avoided crossings between hyperfine states.

Understanding this structure allows us to trap the molecules in a range of internal states. We study the collisional lifetimes of the molecules in such traps for various rotational and hyperfine states, shedding light on the sticky collision issue. Finally, I will describe our plans for imaging and addressing of single molecules in ordered arrays as a basis for quantum simulation.

Michael Holzscheiter (University of New Mexico, Albuquerque)

Wed 24. October 2018 at 14:00

Low Energy Anti-Matter at CERN

In the early 1970s the need for antiproton’s developed in the context of the search for the W and Z Bosons and an antiproton source, collector, and accumulator was constructed. Immediately a group of low energy physicist realized the potential for new physics at lower energies and developed the concept of a Low Energy Antiproton Ring (LEAR) and successfully lobbied the CERN Management into adding such a facility to the offerings of CERN. When eventually the need for high energy antiprotons ceased a shutdown of LEAR was imminent, but the low energy physics community was successful in convincing CERN of the scientific value of a scaled down “stand-alone” machine, the Antiproton Decelerator (AD).

I will describe some of the critical steps in the development from the early thoughts about antiproton production to the commissioning of the AD Ring and then summarize the achievements and goals of the antimatter community in probing the foundation of physics with such a small (compared to the LHC) facility.

Andrea Rodriguez Blanco (Complutense University Madrid)

Tue 02. October 2018 at 14:00

Sideband cooling of a trapped ion using long-wavelength radiation

Sideband cooling is a well established technique that allows the motional states of one or more ions to be cooled below the Doppler cooling limit and ideally close to the ground state |n = 0i. The near vibrational ground state is usually a preliminary condition for many coherent quantum-state manipulations of trapped ions. In quantum computer’s prototypes based on several trapped ions, one of the collective vibrational modes of the ground state is often used as a ”quantum data bus”. This data-bus allows the transfer of quantum information between the different internal states of the trapped ions oscillating in the same mode.

Sideband cooling was initially implemented using laser radiation. The first experiments reached the ground state through an electric quadrupole transition [1] and later on they did it by using a Raman transition [2]. However, for quantum information processing, as the number of trapped ions needs to increase, the optical setup employed for addressing individual qubits from the ensemble becomes complicated. Simpler methods using the well-established and off-the-shelf radiofrecuency (RF) and microwave (MW) technology could be employed instead. So far, new schemes using RF and MW radiation in combination with an oscillating magnetic field have reached a mean phonon number of n̄ = 0.6(1) [3] and with a static magnetic field gradient, the most recent, similar to our implementation, reached a n̄ = 0.30(12) [4]. Here, a static magnetic field gradient [5] allows sidebands transitions between the hyperfine ground states using a RF field in conjuction with MW frequency radiation and a n̄ = 0.13(14) is measured [6]. In this situation, lasers are only used for repumping and the usual Doppler cooling, state preparation and readout of a 171Yb+ ion. Therefore, we demonstrate that it is possible to achieve a near ground state cooling of a trapped ion using long-wavelength radiation with a smaller number of laser beams, which could result in advantage for the scalability of large trapped ion experiments.

  1. F. Diedrich, J.C. Bergquist, W.M. Itano, and D.J. Wineland, Phys. Rev. Lett. 62, 403 (1989).
  2. C. Monroe, D.M. Meekhof, B.E. King, S.R. Jefferts,W. M. Itano, D.J. Wineland, and P. Gould, Phys. Rev. Lett. 75, 4011 (1995).
  3. C. Ospelkaus, U. Warring, Y. Colombe, K.R. Brown, J.M. Amini, D. Leibfried, and D.J. Wineland, Nature 476, 181 (2011).
  4. T. Sriarunothai, G. Shankar Giri, S. Wolk and C. Wunderlich Journal of Modern Optics, 65:5-6, 560-567
  5. F. Mintert and C. Wunderlich, Phys. Rev. Lett. 87, 257904 (2001).
  6. S. Weidt, J. Randall, S.C. Webster, E.D. Standing, A. Rodriguez, A.E. Webb, B. Lekitsch, and W. K. Hensinger, Phys. Rev. Lett. 115, 013002 (2015)

Juanjo Garcia Ripoll (Institute for Fundamental Physics Madrid)

Tue 18. September 2018 at 14:00

Superconducting quantum circuits for quantum optics and quantum computing

In these lectures I will introduce you to the theory of superconducting quantum circuits. In a bottom-up approach, we will explore the effective theory of these circuits, how to develop quantum mechanical models, how they implement microwave cavities, photon waveguides, or qubits. We will then discuss how these elements are put together to study the quantum Rabi model, to do quantum simulation and to implement scalable quantum computers. The lectures will be self contained and accompanied by notes with supporting material, an update of what is now available in the webpage

Koen Vandewal (Hasselt University)

Mon 06. August 2018 at 10:00

Intermolecular Charge-Transfer States for Organic Electronics

Intermolecular charge transfer (CT) states at the interface between electron-donating and electron-accepting (A) materials in organic thin films are characterized by absorption and emission bands within the optical gap of the interfacing materials. Depending on the used donor and acceptor materials, CT states can be very emissive, or generate free carriers at high yield. The former can result in rather efficient organic light emitting diodes, via thermally activated delayed fluorescence, while the latter property is exploited in organic photovoltaic devices and photodetectors. In this contribution, we will discuss the fundamental properties of CT states and link them to organic opto-electronic device performance. We will discuss the influence of intra- and inter-molecular properties, such as the energy of the CT state, the electronic coupling between electron donor and acceptor, the molecular reorganization energy as well as non-radiative triplet states on radiative and non-radiative free carrier recombination. Furthermore, we introduce a new device concept, using an optical cavity resonance effect to boost CT absorption at photon energies below the optical gap of both donor and acceptor, enabling narrow-band, near infrared (NIR) photo-detection. Our findings imply that the power conversion efficiency of organic photovoltaics and maximum achievable detectivities for organic NIR detectors are limited by the presence of high energy vibrational modes and electron-phonon coupling, intrinsic to organic semiconductors.

  1. Vandewal, Koen, et al. Physical Review B 81.12 (2010): 125204.
  2. Vandewal, Koen, et al. Nature materials 13.1 (2014): 63.
  3. Siegmund, Bernhard, et al. nature communications 8 (2017): 15421.
  4. Tang, Zheng, et al. Advanced Materials 29.33 (2017): 1702184.

Kiran Khosla (Imperial College, London)

Tue 12. June 2018 at 14:00

Displacemon electromechanics: how to detect quantum interference in a nanomechanical resonator

Micro-mechanical oscillators are attractive systems to begin probing quantum mechanics at the mesoscopic level. Recent advances in technology are beginning to allow quantum control over the motional degrees of freedom of such micro-mechanical oscillators. Here, I will introduce the 'displacemon' - an electromechanical architecture that couples a vibrating nanobeam, e.g. a carbon nanotube, to a superconducting qubit. This platform can achieve strong and even ultrastrong coupling enabling a variety of quantum protocols, in particular, I'll describe a protocol for generating and measuring quantum interference between two trajectories of the mechanical oscillator. I'll demonstrate the feasibility of generating a spatially distinct quantum superposition state of motion containing more than 10^6 nucleons, and discuss the signatures of a fully quantum (as opposed to classical) oscillator.

Phys. Rev. X 8, 021052 (2018)

Brianna R. Heazlewood (Department of Chemisty, University of Oxford)

Fri 25. May 2018 at 11:00

Into the cold regime: ion-radical collisions

Studying reactions between two unstable species has been an ongoing experimental challenge. I will present our new approach to this old problem: combining a source of cold radicals with Coulomb-crystallised ions held within an ion trap.

Studying ion-radical collisions in this way offers a number of advantages, including the ability to detect reactions with high sensitivity and excellent control over the reaction conditions. Preliminary studies involving charge exchange between Coulomb-crystallised ions held within a linear Paul ion trap and cold neutral molecules will be presented. For quantitative analysis, a mass-sensitive detection method is adopted - with the ejection of all ions onto an external detector at a selected time. This time-of-flight mass spectrometry (ToF-MS) approach removes ambiguity about the identities of dark ions: both the masses and relative numbers of all trapped species at the point of ejection can be ascertained directly from the ToF trace.

Combining ToF-MS detection capabilities with real-time imaging of the Coulomb crystal enables one to examine both the kinetics and the dynamics of ion-neutral reactions. Our source of cold radical species, a Zeeman decelerator, will be described and the clever (in my opinion) way that we gain optimal performance will be explained. Finally, I will present our designs for a combined Zeeman decelerator-ion trap apparatus, and discuss our progress to date.

Adam Deller (UCL)

Wed 18. April 2018 at 13:30

Controlling Rydberg atoms and molecules (and positronium) with electric fields

Many of the properties of atoms or molecules in highly excited Rydberg states have a strong dependence on the principal quantum number, n. Laser excitation to these states can be used to attain long lifetimes, macroscopic classical radii, or extremely large electric dipole moments. Applications that exploit the novel attributes of Rydberg systems are being developed in the fields of quantum information processing, exotic chemistry, and antimatter research. In this talk, I'll provide an overview Rydberg atoms and I will also discuss the process of Rydberg-Stark deceleration with inhomogeneous electric fields. This technique can be employed to exert control over any Rydberg system, including the part-antimatter positronium atom.

Debashree Chowdhury (Ben-Gurion University, Israel)

Wed 14. February 2018 at 14:00

Electron vortex beams and Spintronics

Vortex beams refer to freely-propagating particle beams constituted of electrons or photons, carrying quantized orbital angular momentum (OAM) about their axis of propagation. Allen was the first to forward the theory of optical vortices with intrinsic OAM. The recently proposed concept of electron vortex beams is interesting because electrons carry spin and charge, making EVBs potential candidates for applications ranging from atomic physics to quantum information and spintronics. In this talk I will mainly focus on the spintronics applications of Electron vortex beams.

Farid Shahandeh (CQC2T, Uni Queensland)

Wed 13. December 2017 at 15:00

What Do We Learn About Quantum Correlations From Collaborative Quantum Computing?

Determining whether the correlations between two systems are quantum or classical is fundamental to our understanding of the physical world and our ability to use such correlations for technological applications. The common approach is to ask about the properties of measurement statistics using different types of resources, resulted in the standard classification of quantum correlations in quantum information, namely entanglement [1] and discord [2,3].

Here, we pose the quantum-classical separation problem from a computational perspective and try to provide a consistent solution to it. We ask "what do we infer about quantumness of correlations from the supremacy of collaborative quantum computations?" We investigate the answer to this question within both continuous variable domain (i.e., bosonic systems) [4] and discrete variable domain [5] and find that a separation between classical and quantum correlations is possible from computational viewpoint.

Within both regimes, we show that the global coherence of the input quantum states to the computational models provide the necessary and necessary-and-sufficient resources for the collaborative quantum advantage, respectively. We show that our generalized definition of quantum correlations properly and consistently contains the standard classifications of quantum optics and quantum information. As such, Bell nonlocality, entanglement, discord, and global phase-space nonclassicality [6] are only manifestations of net global coherence. Last but not least, we provide an operational interpretation of such correlations as those allowing two distant parties to increase their respective local quantum computational resources only using locally classical operations and classical communication.

[1] R. F. Werner, Quantum States with Einstein-Podolsky-Rosen Correlations Admitting a Hidden-Variable Model, Phys. Rev. A 40, 4277 (1989).

[2] L. Henderson and V. Vedral, Classical, Quantum, and Total Correlations, J. Phys. A 34, 6899 (2001).

[3] H. Ollivier and W. H. Zurek, Quantum Discord: A Measure of the Quantumness of Correlations, Phys. Rev. Lett. 88, 017901 (2001).

[4] F. Shahandeh, A. P. Lund, and T. C. Ralph, Quantum Correlations in Nonlocal Boson Sampling, Phys. Rev. Lett. 119, 120502 (2017).

[5] F. Shahandeh, A. P. Lund, and T. C. Ralph, Quantum Correlations and Global Coherence in Distributed Quantum Computing, arXiv:1706.00478 [quant-ph].

[6] W. Vogel and D.-G. Welsch, Quantum Optics, (Wiley-VCH, Weinheim, 2006).

Dieter Jaksch (Oxford)

Wed 15. November 2017 at 15:00

Optically driven strongly correlated quantum systems

Recent experimental progress [1,2] indicates that selective and strong optical driving of phonons may generate or enhance ordered phases in strongly correlated quantum materials. This is achieved by driving the system far out of thermal equilibrium on a very short time scale where the dynamics is dominated by coherent quantum evolution. In my talk I will discuss a collection of approaches for gaining a better understanding of the fundamental physical processes that might underpin these experiments. I will focus on the study of driven toy models and also mention novel approaches to the simulation of strongly correlated quantum systems as well as quantum optics based experiments. The long term aim of this work is to help developing optimized methods for optically controlling and steering dynamics far away from thermal equilibrium in quantum matter to induce new functionality.

Specifically, I will consider a one-dimensional driven fermionic Hubbard model in the strongly correlated limit where the onsite interaction dominates over the kinetic energy [3]. The driving is modelled as an alternating periodic modulation of the lattice site energy offsets. I will show how this modulation suppresses tunnelling and induces exchange interactions. The combination of these effects changes the nature of the system into an attractive Luttinger liquid and leads to enhanced fermion pairing in one spatial dimension. I will present results at zero and finite temperatures and discuss the prospect of observing driven out-of-equilibrium superconductivity in this model system. I will then move to novel hybrid quantum-classical approaches for DMFT simulations that promise to yield insights into the driven Hubbard model in higher spatial dimensions.

[1] D. Fausti, R. I. Tobey, N. Dean, S. Kaiser, A. Dienst, M. C. Hoffmann, S. Pyon, T. Takayama, H. Takagi, and A. Cavalleri, Light-Induced Superconductivity in a Stripe-Ordered Cuprate, Science 331, 189 (2011).

[2] M. Mitrano, A. Cantaluppi, D. Nicoletti, S. Kaiser, A. Perucchi, S. Lupi, P. Di Pietro, D. Pontiroli, M. Ricco, S.R. Clark, D. Jaksch and A. Cavalleri, Possible light-induced superconductivity in K3C60 at high temperature, Nature 530, 461-464 (2016).

[3] J. Coulthard, S.R. Clark, S. Al-Assam, A. Cavalleri and D. Jaksch, Enhancement of super-exchange pairing in the periodically-driven Hubbard model, Phys. Rev. B 96, 085104 (2017).

Giuseppe Magnifico (University of Bologna)

Tue 07. November 2017 at 14:00

Quantum Simulation of (1+1)D QED

Simulating quantum physics is still today a very challenging problem due to the very large size of the Hilbert spaces that typically grows exponentially with the degrees of freedom. This property imposes significant limitations in calculating the ground states of quantum many-body Hamiltonians and determing the time evolution. In recent years, a new simulation method, called quantum simulation, have become increasingly popular in order to circumvent these difficulties. The basic idea is very simple: to use some fully controllable quantum system, called quantum simulator, to emulate and to analyze the original problem. We will explore these ideas from a theoretical point of view, focusing on the simulation of Schwinger model for (1+1)D Quantum Electrodynamics. In doing so, we use a new Zn--approach and numerical techniques, such as DMRG, in order to determine the effectiveness of the model in reproducing the main features and phenomenology of the target theory.

Thierry Ferrus (Hitachi Cambridge)

Thu 19. October 2017 at 15:00

Charge qubit states in silicon architectures

Quantum dot architectures have undeniably regained interest for quantum information despite enormous progress in the realisation and the control of both electron and nuclear spin donor-based qubits. Most of the current research concentrates on Metal-Oxide-Semiconductor (MOS) based structures. However, the use of high doped silicon and constrictions provides an alternative way to define metallic-like quantum dots while reducing significantly the number of connections. Our qubit and detector design reflects these ideas. Scalability is further improved by lithographically defining isolated double quantum dots that are used to carry charge qubit states. I will show how, in such particular configuration, qubit states can be read and manipulated with great accuracy by either DC gate or microwave pulses. In particular, I will present both theoretical and experimental investigations, discussing the major differences between doped and MOS-type devices on the operation, the scalability as well as the extremely and surprisingly long coherence times observed.

Part of this work has been supported by the Project for Developing Innovation Systems of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan

Miguel Angel Martin-Delgado (Universidad Complutense Madrid)

Wed 28. June 2017 at 14:00

Self-Correcting Quantum Computers and Lattice Gauge Theories

I review the notions of bare (unprotected) quantum devices (QD), externally protected QDs [1] and internally protected QDs. Quantum topological states are used as a resource to achieve for the first time a fully-fledged quantum device like a quantum computer, including self-correcting initialization, measurements and quantum gates [2]. This construction is based on Topological Color Codes [3,4] which have very nice and powerful transversality properties which allow them to perform quantum tasks like topological quantum distillation, teleportation, dense coding etc. There are recent experimental small realizations of Topological Color Codes using a trapped-ion platform [5]. The underlying physical phenomena in these new quantum devices is the notion of topological order: a new paradigm in strongly correlated systems. We show how quantum topologically protected states can be constructed not only in 2D space but also in higher dimensional systems [6].

1 "Error Threshold for Color Codes and Random 3-Body Ising Models" H. G. Katzgraber, H. Bombin, M. A. Martin-Delgado; Phys. Rev. Lett. 103, 090501 (2009) 2 "Self-Correcting Quantum Computers" H. Bombin, R. W. Chhajlany, M. Horodecki, M.A. Martin-Delgado; New Journal of Physics 15 (5), 055023 (2013). 3 "Topological Quantum Distillation" H. Bombin, M.A. Martin-Delgado; Phys.Rev.Lett. 97 (2006) 180501 4 "Topological Computation without Braiding" H. Bombin, M.A. Martin-Delgado; Phys.Rev.Lett.98:160502, (2007) 5 "Quantum computations on a topologically encoded qubit" D. Nigg, M. Muller, E. A. Martinez, P. Schindler, M. Hennrich, T. Monz, M. A. Martin-Delgado, R. Blatt; Science Vol. 345 no. 6194 pp. 302-305 (2014). 6 "Exact Topological Quantum Order in D=3 and Beyond: Branyons and Brane-Net Condensates" H. Bombin, M.A. Martin-Delgado; Phys.Rev.B75:075103, (2007)

Dylan Owen (Kings College, London)

Wed 10. May 2017 at 15:30

Fluorescence microscopy methods to investigate the biophysical regulation of cell signalling

Fluorescence microscopy is popular in the life sciences due to its molecular specificity and non-invasiveness. Here, I will outline three methods we are using to study how biophysical mechanisms regulate the activation of T cells, a key regulator of the adaptive immune system.

Firstly, single-molecule super-resolution microscopy combined with novel statistical analysis which we use to describe the nanoscale clustering of cell surface molecules and the nanoscale ultrastructure of the cell skeleton. Second, structured illumination super-resolution microscopy combined with image correlation approaches to quantify molecular flows in cells including those of the cell skeleton and the cell membrane. Finally, environmentally sensitive membrane dyes which report on their local biophysical and biochemical environments to study molecular organisation in the cell membrane. Together, these methods show how macroscale events - such as an immune response - can be regulated by nanoscale spatio-temporal molecular organisation.

Juan Garrahan (Nottingham)

Wed 15. March 2017 at 14:00

Slow relaxation, glassiness and non-ergodicity in quantum many-body systems

I will describe the applicability to problems of slow relaxation and non-equilibrium in the dynamics of quantum many-body systems of concepts more frequently associated with classical soft matter systems such as glasses. I will discuss how quantum slow dynamics arises from local dynamical constraints, how collective relaxation is a phenomenon dominated by spatial fluctuations in the dynamics, and whether quantum non-ergodicity - termed many-body localisation - can arise in systems without disorder. I will also discuss experimentally relevant issues such as the effect of dissipation and how to probe the growth of entanglement and coherence in these systems.

Hendrik Ulbricht (Southampton)

Wed 08. February 2017 at 15:30

Prospects for using levitated optomechanics to test quantum mechanics and gravity

We will discuss our trapping and cooling experiments of optically levitated nanoparticles [1]. We will report on the cooling of all translational motional degrees of freedom of a single trapped silica particle to ~1mK simultaneously at vacuum of 10-5 mbar using a parabolic mirror to form the optical trap. We will further report on the squeezing of a thermal motional state of the trapped particle by rapid switch of the trap frequency [2].

We will further discuss ideas to experimentally test quantum mechanics by means of collapse models [3] by both matter-wave interferometry [4] and non-interferometric methods [5]. While first experimental bounds by non-interferometric tests have been achieved during the last year by a number of different experiments [4], we at Southampton work on setting up the Nanoparticle Talbot Interferometer (NaTalI) to test the quantum superposition principle directly for one million atomic mass unit particles.

We will further discuss some ideas to probe the interplay between quantum mechanics and gravitation by (levitated) optomechanics experiments. One idea is to seek experimental evidence about the fundamentally quantum vs classical nature of gravity by using the torsional motion of a non-spherical trapped particle, while another idea is to test the existence of a gravity related shift of energy levels of the mechanical harmonic oscillator, which is predicted by semi-classical gravity (the so-called Schrdinger-Newton equation) [6].

  1. Vovrosh, J., M. Rashid, D. Hempston, J. Bateman, and H. Ulbricht, Controlling the Motion of a Nanoparticle Trapped in Vacuum, arXiv:1603.02917 (2016).
  2. Rashid, M., T. Tufarelli, J. Bateman, J. Vovrosh, D. Hempston,M. S. Kim, and H. Ulbricht, Experimental Realisation of a Thermal Squeezed State of Levitated Optomechanics, Phys. Rev. Lett. 117, 273601 (2016)
  3. Bassi, A., K. Lochan, S. Satin, T.P. Singh, and H. Ulbricht, Models of Wave-function Collapse, Underlying Theories, and Experimental Tests, Rev. Mod. Phys. 85, 471 - 527 (2013)
  4. Bateman, J., S. Nimmrichter, K. Hornberger, and H. Ulbricht, Near-field interferometry of a free-falling nanoparticle from a point-like source, Nat. Com. 5, 4788 (2014); Wan, C., et al. Free Nano-Object Ramsey Interferometry for Large Quantum Superpositions, Phys. Rev. Lett. 117, 143003 (2016).
  5. Bahrami, M., M. Paternostro, A. Bassi, and H. Ulbricht, Non-interferometric Test of Collapse Models in Optomechanical Systems, Phys. Rev. Lett. 112, 210404 (2014); Bera, S., B. Motwani, T.P. Singh, and H. Ulbricht, A proposal for the experimental detection of CSL induced random walk, Sci. Rep. 5, 7664 (2015).
  6. Grossardt, A., J. Bateman, H. Ulbricht, and A. Bassi, Optomechanical test of the Schroedinger-Newton equation, Phys. Rev. D 93, 096003 (2016).

Mauricio Gutierrez (Swansea)

Fri 27. January 2017 at 14:00

Coherent vs. incoherent noise in quantum computers: how effective is quantum error correction?

One of the main challenges to the construction of a scalable quantum computer is the extreme sensitivity of quantum information to environmental noise and instrumental imperfections. On the theoretical front, several strategies have been proposed to mitigate errors and perform successful computations in the presence of noise. Most of these quantum error correction (QEC) strategies have been designed for incoherent noise, which typically arises from stochastic interactions with the environment. Recently, it has been pointed out by several authors that coherent errors, which arise from instrumental miscalibrations, can corrupt quantum information to a much higher degree than incoherent errors. It is not clear whether or not traditional QEC methods can be protective against this type of noise. To tackle this problem, we have devised a simulation technique to accurately measure how effective QEC is to mitigate coherent errors. We have found that QEC transforms noise from coherent to effectively semi-coherent [1]. Furthermore, ongoing work in our group suggests that subsequent levels of QEC can transform coherent noise to completely incoherent. This means that, although coherent noise can be extremely deleterious to quantum information, a clever application of QEC can reduce the noise to tolerable levels, which relaxes the stringent experimental demands needed to build a quantum computer.

[1] M. Gutierrez et al., Phys. Rev. A 94, 042338 (2016)

Alessio Serafini (UCL)

Wed 18. January 2017 at 15:30

Unravelling the noise - The estimation of decoherence rates under continuous monitoring

The distinction between fundamental noise (such as that induced by effective collapse or quantum gravity models) and environmental one (due to the coupling to a well identified environment) is a challenging objective, since the two forms of noise have identical dynamical consequences.

Inspired by the notion that environmental noise is in principle observable, whilst fundamental noise would not be, we study the estimation of the diffusion parameter induced by wave function collapse models under continuous monitoring of the environment. We will thus show that monitoring can break the symmetry between the roles of fundamental and environmental noise parameters, and thus improve the upper bounds one can put on the former.

In this pedagogical talk, we will derive our result in detail from first principles, taking into account finite measurement efficiencies and, in order to quantify the advantage granted by monitoring, also analysing the quantum Fisher information associated with a diffusion parameter.

Ifan G. Hughes (Durham)

Fri 16. December 2016 at 14:00

Quantum Optics in alkali-metal thermal vapours

The study of light propagation through thermal atomic vapours subject to external magnetic fields is a flourishing area of research. At Durham we have spent 15 years studying the spectroscopy of alkali-metal vapours, culminating in the publication of our electric susceptibility code ElecSus (Zentile et al. Computer Physics Communications 189 162-174 (2015)). The applications range from devices (a compact optical isolator, narrow-line filters) to fundamental physics (measuring the cooperative Lamb shift, a possible new method to measure Boltzmann's constant).

In the talk I will describe experimental and theoretical work to model the electric susceptibility of a vapour of alkali-metal atoms; and finish with an outlook for cooperative quantum optics in thermal vapours.

Hamid Ohadi (Cambridge)

Wed 07. December 2016 at 15:30

Peculiar spin properties of exciton-polariton condensates

While ultracold atoms have been very successful in probing closed equilibrium condensed matter phenomena, open non-equilibrium quantum systems have attracted a strong and growing interest recently because of their rich dynamics and nontrivial steady states. Exciton-polaritons (polaritons) have emerged as a prime candidate for the non-equilibrium system of interacting bosons.

Polaritons are mixed light-matter bosons resulting from the strong coupling of photons in a microcavity and excitons in a quantum well which can condense into macroscopically coherent many-body states. As a prime example of the non-equilibrium nature of polariton condensates, we have shown recently that polariton condensates can spontaneously magnetize, and we can control their spin optically and electronically. Interestingly, the direction of the spin of two coupled condensates can be also controllably aligned (or anti-aligned). Hence, a lattice of polariton condensates is expected to model a non-equilibrium interacting spin system with unusual properties. I will address this and show you some very interesting and surprising recent results from our labs.

Alejandro Bermudez (Swansea)

Wed 23. November 2016 at 14:00

Topological Insulators: Condensed Matter, High-Energy Physics, and AMO

In this talk, I will review the main properties of topological insulators, i.e. holographic phases of matter with an insulating bulk but conducting boundaries, characterised by a topological invariant.

I will emphasise the connection between condensed matter and lattice Gauge theory concepts, and review possible implementations in the field of atomic atomic, molecular, and optical (AMO) physics.

This connection allows us to introduce lower-dimensional 'toy' models where strong-correlation effects brought by interactions can be understood both analytic and numerically, and where cold-atom experiments can be used to test our predictions.

Matthew Himsworth (Southampton)

Wed 16. November 2016 at 15:30

Integrated Atom Chips

Cold atom experiments come in many forms, usually in large scale vacuum chambers too bulky for practical devices beyond the laboratory, but many are being translated to more compact forms known as 'atom chips'. These are microfabricated wires patterned onto a substrate through which currents are passed to form various magnetic traps for atoms. Currently these chips, which are no larger than a postage stamp, are still housed in large vacuum chambers surrounded by a vast array of optics, laser, detectors and control electronics. If Quantum Technology is to truly make a significant impact we need to focus on miniaturizing and integrating this infrastructure as well. We aim to do this not with scaled-down copies of conventional components, but with mass-producable planar fabrication techniques, developed for semiconductor devices and MEMS, which we adapt to perform the roles of large scale apparatus.

Amit Kumar Pal (Swansea)

Wed 09. November 2016 at 14:00

Can one freeze quantum correlations?

Protecting resources in the form of quantum correlations, such as entanglement and quantum discord, against environmental noise, is of paramount importance towards the development of quantum technology. In this talk, we discuss how quantum correlations can be "frozen" over time, despite their exposure to environmental noise. We show that bipartite quantum correlations, such as quantum discord and other "discord-like" quantities, can be frozen by properly tuning the initial state subjected to the noise. We discuss a possible situation where bipartite entanglement, although being more fragile than the "discord-like" quantities, can be frozen by a suitable choice of quantum many-body system. We also demonstrate that the freezing of entanglement is a scale-invariant phenomenon in specific phases of some quantum spin models.

Daniel Oi (Strathclyde)

Wed 26. October 2016 at 16:00

CubeSats for Quantum Science (Fun) and Technology (Profit)

Bringing quantum science and technology to the space frontier offers exciting prospects for both fundamental physics and applications such as long-range secure communication and space-borne quantum probes for inertial sensing with enhanced accuracy and sensitivity. But despite promising proposals to exploit the significant advantages of space quantum missions, large-scale quantum test beds in space are yet to be realised due to the high costs and lead times of traditional 'Big Space' satellite development. But the 'small space' revolution, spearheaded by the rise of nanosatellites such as CubeSats, is an opportunity to greatly accelerate the progress of quantum space missions by providing easy and affordable access to space and encouraging agile development. We review space quantum science and technology, CubeSats and their rapidly developing capabilities and how they can be used to advance quantum satellite systems.

Daniel Burgarth (Aberystwyth)

Wed 19. October 2016 at 15:30

Protect Schrödingers Cat or disprove his Equation?

Preserving Quantum Information (coherence) is the main technical challenge on the road to Quantum Technology. The purpose of this talk is to introduce the noise models one commonly studies, and the countermeasures against decoherence which have been brought forward in the field of quantum control. We will try to define the jargon "non-Markovian" which is commonly discussed in this context and observe some intriguing mathematical contradictions. These will lead us to suggest a test for the validity of Schrödinger's Equation.


If you would like to schedule a talk, or have any queries, please contact James Bateman


Vivan Tower 413
Department of Physics
Singleton Campus
Swansea University