Quantum talks archive

Find out about our past quantum talks.

21 November 2019 - Andrew Groszek (Newcastle University) Large Scale Flows in Two-Dimensional Quantum Turbulence.

Non-equilibirum interacting systems can evolve to exhibit large-scale structure and order. In two-dimensional turbulent flow the seemingly random swirling motion of a fluid can evolve towards persistent large-scale vortices. To explain such behaviour, Lars Onsager proposed a statistical hydrodynamic model based on quantised vortices. Our work provides an experimental confirmation of Onsager's model. We drag a grid barrier through an oblate superfluid Bose-Einstein condensate to generate non-equilibrium distributions of quantised vortices. We observe signatures of an inverse energy cascade driven by the "evaporative heating" of these vortices, which leads to steady-state vortex configurations characterised by negative absolute temperatures. We measure these temperatures directly using our recently developed thermometry technique for two-dimensional superfluid turbulence. Complementary observations of negative temperature vortext states have also recently been presented in a similar experiment by Gauthier et al.

7 November 2019 - Dr Rachel Godul (National Physics Laboratory) Optical Atomic Clocks for Testing Fundamental Physics.

For thousands of years, man used the rotation of the Earth as a reference for timekeeping. But the modern world requires far greater precision and the advent of atomic clocks has enabled fractional uncertainties in the realisation of the second to improve by many orders of magnitude. With ever improved accuracy in measurements of time and frequency, it also becomes possible to test fundamental physics at previously inscrutable levels. This talk will present measurements from optical clocks at the National Physics Laboratory that have been used to search for time-variation of fundamental constants and also to place constraints on couplings between Dark Matter and the fields of the Standard Model.

17 October 2019 - Ben Sauer (Imperial College) Direct Laser Cooling of Molecules.

Direct laser cooling techniques that have been developed for atoms can also be applied to certain molecules. Physicists at Imperial College have been workng on cooling of CaF and YbF; diatomic molecules for which quasi-closed transitions can be found. Ben will review the techniques they use and discuss the challenges compared with laser cooling of atoms. He'll discuss their results and in particular how their  laser cooling techniques will enable the next generation of experiments to measure the electron electric dipole moment.

1 August 2019 - Dr Ben Lanyon (University of Innsbruck) Light-matter Entanglement Over 50km of Optical Fibre.

When shared between remote locations, entanglement opens up fundamentally new capabilities for science and technology. Envisioned quantum networks use light to distribute entanglement between their remote matter-based quantum nodes. In this short talk, I will present our observation of entanglement between matter (a trapped ion) and light (a photon) over 50 km of optical fibre: two orders of magnitude further than the state of the art and a practical distance to start building large-scale quantum networks. Our methods include an efficient source of ion-photon entanglement via cavity-QED techniques (0.5 probability on-demand fibre-coupled photon from the ion) and a single photon quantum frequency converter to the 1550 nm telecom C band (0.25 fibre-coupled device efficiency). Modestly optimising and duplicating our system could allow for 100 km-spaced ion-ion entanglement at rates over 1 Hz. Our results therefore show a path to entangling remote registers of quantum-logic capable trapped-ion qubits, and the optical atomic clock transitions that they contain, spaced by hundreds of kilometres.

15 May 2019 - Professor Rainer Blatt (University of Innsbruck) The Quantum Way of Doing Computations.

Since the mid-nineties of the 20th century, it became apparent that one of the centuries' most important technological inventions, computers in general and many of their applications could possibly be further enhanced by using operations based on quantum physics. Computations, whether they happen in our heads or with any computational device, always rely on real physical devices and processes. Data input, data representation in a memory, data manipulation using algorithms and finally, data output, require physical realizations with devices and practical procedures. Building a quantum computer then requires the implementation of quantum bits (qubits) as storage sites for quantum information, quantum registers and quantum gates for data handling and processing as well as the development of quantum algorithms. In this talk, the basic functional principle of a quantum computer will be reviewed. It will be shown how strings of trapped ions can be used to build a quantum information processor and how basic computations can be performed using quantum techniques. The quantum way of doing computations will be illustrated with analog and digital quantum simulations. Ways towards scaling the ion-trap quantum processor will be discussed.

16 May 2019 - Ana Rakonjac (Durham University) Towards Atom Interferometry with Bright Solitary Matter Waves.

Performing interferometry with atoms instead of light holds great promise as the basis for a new generation of sensors. Bose-Einstein condensates (BECs) are excellent candidates for atom interferometry due to their wave-like nature, superfluid properties, and the ability to manipulate them coherently. Many interferometry protocols have been proposed theoretically, and there is presently much experimental effort in implementing novel interferometry schemes, as well as miniaturising atom interferometers for practical use as sensing devices. One such scheme makes use of bright solitary matter waves, or solitons, formed by manipulating interatomic interactions in BECs to create long-lived compact matter wavepackets. Solitons can propagate macroscopic distances without dispersion, making them ideal candidates for use in a number of interferometer geometries. A crucial component of any interferometer is a coherent beam splitter. For solitons, a beam splitter can be formed by a narrow repulsive barrier, where a soliton incident on the barrier is split into two. After allowing the two daughter solitons to oscillate in a weak harmonic potential, the solitons recombine on the same barrier. In the appropriate regime, the recombination is coherent, with any phase accumulation along one path resulting in a population difference in each path after recombination. In practice, there are other factors that influence the outcome. In this talk, I will discuss our efforts to implement a proof-of-principle atom interferometer using bright solitary matter waves and the experimental challenges involved.

9 May 2019 - Brianna Heazlewood (University of Oxford) Cold Ion-neutral Reactions in Coulomb Crystals.

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.

4 April 2019 - Vera Schafer (University of Oxford) Fast Entangling Gates with Trapped Ions.

Trapped ion qubits are one of the most promising candidates for scalable quantum computing. Entangling gates with trapped ions achieve higher fidelities than in any other system, but are typically performed in an adiabatic regime, where the motional frequencies of the ions in the trap limit the gate speed. Many schemes have been proposed to overcome these limitations, but have only now been successfully implemented. We use amplitude-shaped cw-pulses to perform entangling gates significantly faster than the speed limit for conventional gate mechanisms. At these gate speeds, the motional modes are not spectrally isolated, leading to entanglement with both motional modes sensitively depending on the optical phase of the control fields. We demonstrate gates with fidelity F = 99.8% in 1.6 µs - over an order of magnitude faster than previous trapped ion gates of smiliar fidelity. We also perform entanglement generation for gate times as short as 480 ns - this is below a single motional period of the ions.

2 April 2019 - Ryan Willets (University of Sussex) Single Microwave Photon Detection.

Ryan will start with an introduction to Penning Traps and move on to describe quantum-non-demolition measurements of multiple single microwave photons. While these measurements have been proven with larger Penning Traps, they have yet to be attempted with a scalable Penning Trap.

27 March 2019 - Martina Knoop (CNRS/Université d'Aix-Marseille) Precision Spectroscopy with Large Ion Clouds.

Trapped ions are at the heart of many spectacular advances in recent years, in particular regarding high-resolution spectroscopy. They serve as elementary bricks in atomic clocks, quantum information, and the verification of the variation of fundemental constants. Due to the advanced control of the internal and external degrees of freedom of stored ions, they are perfectly adapted to be used as model systems for quantum and classical problems. Laser cooling and individual addressing, detection, and manipulation of single atoms have paved the way to a large variety of important applications and fundamental experiments. I will present some key experiments based on recent work that is done in my group in particular with large ion clouds. I will insist on the recent realisation of a three-photon coherent population trapping protocol. I will discuss precision and robustness of this technique and also the technical aspect of phase-locking three independent lasers by means of an optical frequency comb.

26 March 2019 - Tim James (University of Sussex) The Two Colour Magneto Optical Trap.

Tim will explore how a second cooling frequency can improve the number of atoms trapped in a magneto-optical trap (MOT). He'll explain what a "two colour" MOT is and how it differs from the "single colour" MOT. Using experimental results, he'll cover some basic theoretical ideas around the two colour MOT.

5 March 2019 - Juan Sebastian Totero Gongero (University of Sussex) Complexity-driven Photonics: Collective Interactions and Spontaneous Synchronisation in Nonlinear Photonic Systems.

Complex systems are ensembles of randomly interconnected elements where mutual interactions enable unexpected dynamics and behaviours. These systems are abundant in our daily experience: typical examples are the human brain, society, biological ecosystems, and finance. In the last century, researchers from different disciplines have investigated the fundamental properties of complex systems, unveiling fascinating and counterintuitive dynamics. Due to its ultrafast time scale, nonlinear photonics has recently emerged as an ideal playground to harness these complex interactions to develop advanced devices. In this presentation, I will introduce some of the concepts underlying the field of complexity-driven photonics. In particular, I will discuss how in our laboratory we are employing the "spontaneous synchronisation" of interacting optical waves to design ultrafast pulsed lasers, quantum information sources and brain-inspired optical computing devices.

27 February 2019 - Tracy Northup (University of Innsbruck) Trapped-ion Interfaces for Quantum Networks.

By coupling trapped ions to the mode of an optical resonator, we can construct a coherent interface between single ions and single photons. I will discuss two applications of such an interface. First, an ion can be used as a quantum sensor to probe the light field in the resonator; Ramsey spectroscopy of the ion enables us to reconstruct the photon number distribution interacting with the ion. Second, quantum information can be transferred from ions onto photons for distribution across a quantum network. Probabilistic and deterministic realizations of a network interface will be introduced, based on the building blocks of ion-photon entanglement and ion-photon state transfer. These experiments face significant challenges on the road to a scalable multi-node network, such as decoherence of the ion and losses in photonic channels. I will outline recent proposals to address these challenges.

26 February 2019 - Seokjun Hong (University of Sussex) Microfabrication of Surface Ion Trap Chips.

Seokjun will start with a brief introduction of qubit platform and the history of ion trap structures. He will move on to focus on the detailed microfabrication processes required for advanced surface ion traps.

5 February 2019 - Harry Bostock (University of Sussex) Quantum Sensing using Trapped Ions.

Much has been seen of trapped ions as a method for quantum computing, but one exciting new application for this technology is using them for radio frequency, microwave, and static field sensing. Harry will show how trapped ions can be used as quantum sensors and how they have the potential to outclass both well-established classical sensors and other quantum sensors.