Sussex Quantum Seminars

Some of our recent guest speakers

Professor Giacomo Scalari, Institute for Quantum Electronics at ETH Zurich

Title: High performance on-chip THz frequency combs and detectors based on quantum cascade lasers

Abstract: Recently, THz on-chip quantum-cascade-laser (QCL) sources reached operating temperatures above 200 K, unlocking the use of compact thermoelectric coolers and offering the possibility of filling the lack sources in a spectral region were no table compact source is available. In this seminar, I will present a review of the work done at ETH on THz quantum cascade lasers operating at high temperatures and THz quantum cascade frequency comb sources. Pulsed operation up to 210 K for two-well structures at 4 THz  were obtained, enabling the QCL to be operated on a thermoelectric cooler in combination with a room temperature detector.

Quantum cascade lasers are emerging as well as powerful and compact sources for frequency comb generation in the mid-IR and THz. I will discuss THz combs with spectral coverage in excess of 1 THz centered at 3 THz and operating at 80 K . Particularly, I will present a new platform for planarized THz photonics that includes THz combs and also THz detectors exploiting regenerative amplification, together with dispersion compensated ring lasers for soliton formation. SWIFTS measurements allowing the temporal reconstruction of the THz waveforms will be presented, showing a transition from FM to AM mode-clocking as a function of RF driving.

Dr Giulia Marcucci, Apoha Ltd, London

Title: Learning at the edge of chaos - the inner link between complexity, nonlinear waves, and neuromorphic computing

Abstract: Nonlinear waves' historical role in developing the science of complexity and their physical feature of being widespread in optics and hydrodynamics establish a bridge between two diverse but fundamental fields: nonlinear physics and computational science. Such a link has been opening an endless number of new research routes. Many relevant results on nonlinear waves in photonics and acoustics have assumed major significance in the foundation of new computing models.

In this seminar, I will first report my work on the control of complex nonlinear regimes through topological invariants in photorefractive crystals. Such analysis represents a groundwork for enabling nonlinear waves to do computation, a feature that arises efficiently only when the wave reservoir is at the edge of chaos. Indeed, when waves are both highly nonlinear and controllable, the wave reservoir has two essential properties: given two distinct but similar inputs, their outputs are always distinguishable but never divergent. To demonstrate it, I will present my last works on the engineering of neuromorphic computers, by wave reservoirs.

Professor Claudio Paoloni, Lancaster University

Title: High capacity sub-THz wireless networks enabled by travelling- wave tubes

 Absract: The substantial increase of internet traffic forecasted in 5G and 6G exceeds the capacity of the actual wireless networks at sub-6 GHz and low millimetre waves. The sub-THz spectrum (90 – 300 GHz) has very wide frequency bands to support tens of gigabit per second (Gb/s) not yet exploited due the high path loss, rain attenuation and not mature technology. The low transmission power from solid state amplifiers at those frequencies is not sufficient to ensure long range with high signal-to-noise ratio for supporting high data rate. This is even more critical in case of distribution in point to multipoint by a low gain antenna. Sub-THz Traveling Wave Tubes (TWTs) have been demonstrated as a promising solution to generate transmission power at Watt level, suitable for enabling long range high capacity links.

The talk will present the latest result of a wireless system with D-band (141 – 174.8 GHz) point to multipoint and point to point distribution and G-band (275 – 305 GHz) point to point transport. A discussion at system and component level of sub-THz transmission hubs, terminals and TWTs will highlight the technology challenges of sub-THz spectrum.

Dr Giovanni Barontini, University of Birmingham

Title: QSNET - A network of clocks for measuring the stability of fundamental constants

Abstract: I will discuss the QSNET project, that aims to build a network of atomic and molecular clocks in the UK to achieve unprecedented sensitivity in testing variations of the fine structure constant, α, and the electron-to-proton mass ratio, μ. This in turn will allow us to either discover that fundamental constants are actually not constant, or to provide more stringent constraints on a wide range of fundamental and phenomenological "new physics" models. These include models of dark energy, ultra-light dark matter and grand unification models. The project currently includes the National Physical Laboratory, the University of Sussex, the Imperial College London, the University of Birmingham, and several international partners. I will discuss more in detail the plans of the Birmingham node, where we are building a clock based on highly charged ions of Californium, that is expected to improve our sensitivity to variations of α by orders of magnitude.

Dr François Leo, Université Libre de Bruxelles

Title: Temporal solitons in coherently driven active cavities

Abstract: Temporal dissipative solitons are short optical pulses that propagate indefinitely in a resonator. They have been extensively investigated in passive resonators and lasers. In my talk, I will discuss soliton formation in a hybrid system which consists in a coherently driven active cavity pumped below the lasing threshold. I will show how this novel system allows for the formation of high power, stable soliton trains. This also opens novel avenues for the investigation of new types of solitons such as parametrically driven solitons which have the potential to be used as spins in Ising machines. I will also discuss how solitons can be harnessed for analogs of quantum effects such as Bloch oscillations.

Professor Simon Cornish, Durham University

Title: Adventures in quantum science with ultracold polar molecules

Abstract:  Ultracold 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 relate some of the adventures we have had en route to this ambitious goal.

I will first 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 and to enhance the rotational coherence through a judicious choice of internal state and intensity. We use this capability to study the collisional lifetimes of the trapped molecules for various rotational and hyperfine states, shedding light on the sticky collision issue. Finally, I will report some recent work on engineering robust storage qubits using hyperfine states of the molecule where we observed coherence times > 6.9 s using Ramsey interferometry. As an outlook, I will outline our plans for implementing magic-wavelength optical traps to achieve similar coherence times for rotation-state superpositions and will describe new experiments to image and address single molecules in ordered arrays as a basis for quantum simulation.

Dr Jesús Rubio, University of Exeter

Title: Precision matters - a journey from quantum thermometry to the quantum estimation of scales

Abstract: Whether quantum technologies are ultimately successful will crucially depend on our ability to perform extremely precise measurements. To achieve this, detailed knowledge of the ultimate precision limits allowed by nature is required. Additionally, an efficient and systematic procedure to connect theory-driven estimators with experimental data sets is highly desirable. During the first part of this talk I address both of these problems within the context of quantum thermometry, a framework for the precise measurement of temperatures in ultracold atom (and other) systems. It is shown that, in the absence of any prior knowledge, and using Bayesian principles, the ultimate precision limits for temperature estimation are necessarily expressed in terms of a logarithmic error. Moreover, this leads to an operational rule to map experimental data sets – of any size – to an optimal temperature reading. Its potential application in thermometric experiments is further illustrated by simulating energy and position measurement records. In the second part of this talk I perform a deeper analysis of the mathematics of quantum thermometry, decoupling the underlying estimation theory from its thermodynamic origin. I show that the primary assumption behind logarithmic errors – from where the general framework for quantum thermometry follows – is simply invariance under changes of scale. On the basis of this assumption, I derive a neat framework for the precise estimation of any quantity playing the role of a scale in physics. I conclude by arguing that the quantum estimation of scales completes a trio of theories for the most elementary quantities that one could possibly measure: phases, locations and scales. 

Main reference: J. Rubio el al., Phys. Rev. Lett., 127:190402 (2021)

Professor Kevin Weatherill, Durham University

Title: Rydberg Quantum Technologies

Abstract: Rydberg atoms are highly excited atoms with exaggerated properties. In recent years, Rydberg atoms have emerged as a promising platform for numerous quantum technologies, ranging from quantum computation and simulation, single photon sources, RF communications and SI-traceable standards for electric fields. In this talk, I will explain how the properties of Rydberg atoms make them advantageous for such applications and I will present the results from two recent experiments at Durham. [1] High speed terahertz imaging in thermal atoms that achieves frame rates that are orders of magnitude faster than other terahertz sensors. [2] Collectively encoded qubits in cold-atom ensembles that demonstrate coherence properties that are robust to atom loss and electric field noise.

[1] L. A. Downes et al. Physical Review X. 10, 011027 (2020)

[2] N. L. R. Spong et al. Phys. Rev. Lett. 127, 063604 (2021)