Quantum talks archive
Browse our archive for previous talks from our quantum researchers.
Cavity Assisted Ion-Photon Entanglement
Adrien Amour (Ion Trap Cavity-QED and Molecular Physics group)
7 May 2024
The long coherence time and high gate fidelities demonstrated using trapped ions have shown them to be excellent qubits for quantum computing. Increasing the number of ions on which high-fidelity two-qubit gates can be performed, however, is a significant obstacle to building a large-scale ion trap-based quantum information processor (QIP). The distributed quantum computation architecture solves this problem by linking small-scale QIPs to form a large-scale quantum computing network. Using photons as flying qubits is the natural choice for this link and enables any node-to-any-node interconnectivity.
One process to establish inter-node entanglements is a probabilistic scheme. To establish entanglement between nodes, ions are initially entangled in different nodes with photons before performing a Bell state measurement on a pair of photons, which projects the two ions onto an entangled state. Traditionally this has been achieved using photons collected via spontaneous emission.
Alternatively, cavities may be employed to stimulate photon production via cavity-stimulated Raman transitions. Through this approach, a superior rate of photon collection can be achieved and control of both the temporal and spatial properties of the produced photons is possible.
Previous research within the group has demonstrated schemes that produce photons with greater indistinguishability, which are more robust against birefringence-induced decoherence. These improvements have been achieved through state selection and time-bin encoding, respectively. The aim of this project is to build upon this research by producing Ion-photon entangled pairs.
Barium Ions at Sussex
Parsa Rahimi (Ion Quantum Technology group)
26 March 2024
In this presentation, we explore the process of loading Barium into surface ion traps using laser ablation of a Barium Chloride target. We conduct time-of-flight analysis on the ablated plume through fluorescence spectroscopy with a photomultiplier tube. Additionally, we investigate the photoionization of atomic Barium through resonance-enhanced multiphoton ionization. Finally, we discuss the technique of Doppler cooling applied to the lambda structure of the ionic state.
The Magnetic Inverse Problem – Mathematical Detective Work for Electric Currents
Michael Woodley (Quantum Systems and Devices group)
27 February 2024
From neuroimaging to battery characterisation, it can be very instructive to non-invasively image a source of electric current by reconstructing it from the magnetic field that it produces. This is an example of a so-called inverse problem – inferring causes from effects. In this talk, I will introduce this magnetic inverse problem, and how it can be used for battery imaging, in particular. I will also talk about when this approach fails – i.e., non-invertible (or singular) situations – and what may be done to approximate the current density in these cases.
An Ion Trap Quantum Processor with Integrated Ion-Photon Interface
Maoling Chu (Ion Trap Cavity - QED and Molecular Physics group)
30 January 2024
The aim of this project is to build a quantum computing processor with integrated ion-photon interface. It consists of an ion trap with zones for ion loading, QIP and a zone with an integrated optical cavity for enhanced communication. The electrode structure is designed for dual species operation, ion swapping and ion chain splitting. To achieve highly efficient high-fidelity quantum communication between processors, the system is equipped with an integrated cavity, strongly coupling to the trapped ion. To realize this, we designed a chip, which was manufactured using femtosecond laser induced selective etching (FLISE) from a fused silica substrate, and subsequently gold coated. Employing trenches between the electrodes the chip can be metalised without masks. The cavity is formed of fused silica rods instead of optical fibres as has been used previously in order to improve the photon collection efficiency. In previous works, researchers have reported effective photonic entanglement by using high-numerical-aperture lens’ to couple two ions’ qubits into single-mode optical fibres to attain high rate and fidelity. For our system, we expect significantly higher entanglement rates with high fidelity due to strong coupling operation.
- 2023 quantum talks
Smart Skins based on Assembled Piezoresistive Networks of Sustainable Graphene Microcapsules for High Precision Health Diagnostics
Adel Aljarid (Materials Physics group)
5 December 2023
The environmental impact of plastic waste has had a profound effect on our livelihoods and there is a need for future plastic-based epidermal electronics to trend toward more sustainable approaches. Infusing graphene into the culinary process of seaweed spherification produces core-shell, food-based nanocomposites with properties exhibiting a remarkably high degree of tunability. Unusually, mechanical, electrical, and electromechanical metrics all became decoupled from one another, allowing for each to be individually tuned. This leads to the formation of a general electromechanical model which presents a universal electronic blueprint for enhanced performances. Through this model, performance optimization and system miniaturization are enabled, with gauge factors (G) >108 for capsule diameters (D) ≈290 µm and produced at a record rate of >100 samples per second. When coalesced into quasi-2D planar networks, microcapsules form the basis of discrete, recyclable electronic smart skins with areal independent sensitives for muscular, breathing, pulse, and blood pressure measurements in real-time.
Developing the Bose-Einstein condensate microscope (BEC-M)
Poppy Joshi (Quantum Systems and Devices group)
21 November 2023
The Bose-Einstein condensate microscope (BEC-M) is a highly sensitive atomic probe which can be used to detect very small changes in magnetic fields, with typical sensitivity of order nT and a spatial resolution of order µm. The idea of BEC-enabled microscopy started in 2006 following the observation of the fragmentation of a BEC gas above an atom chip . Further developments were made in 2017 where microfabricated wire patterns were specifically designed to test the capabilities of the BEC as a magnetometer. The BEC-M could become a powerful tool for mapping current flow to identify hotspots in live nanomaterial networks which could aid in the development of flexible electronics. We have just taken the first BEC-M measurement of a nanomaterial (carbon nanotubes) where we were able to identify off axis current flow. The next steps for this experiment will be to perform the same measurement on silver nanowires, and skin cells as well as implementing atom transport.
Towards High-Fidelity Entanglement Gates on Microfabricated Ion-Traps with Embedded Current-Carrying Wires
Petros Zantis (Ion Quantum Technology group)
7 November 2023
Trapped ions have proved to be a promising way of realising a large-scale quantum computer. This is due to their highly stable and well-resolved energy levels leading to long coherence times. They also allow for simple reproducibility and modular architectures which is crucial for a scalable, universal quantum computer. Our blueprint for a trapped-ion based quantum computer outlines operating with global microwave (MW) fields to dress the ground-state hyperfine manifold of 171Yb+ ions. By applying individually controlled static (DC) voltages, ions can be effectively shuttled between modules, while modulated radio-frequency (RF) signals are utilised to facilitate quantum logic gate operations.
Borrowing knowledge from the widely successful semiconductor industry, the development of microfabricated ion traps has allowed the advance of preceding work onto silicon chips with integrated technologies, such as embedded current-carrying wires (CCWs) which provide a controllable magnetic field gradient. Naturally, the next step in further developing and operating our quantum computer prototype, is the demonstration of high-fidelity gate operations on these novel microfabricated ion-trap chips, which serve as the modules of the scalable device. Gate infidelities below the fault-tolerant threshold would in turn allow us to perform logical operations and implement algorithms such as the surface code, a quantum error-correction scheme.
Towards the Implementation of the Quantum Illumination Protocol using a Trapped Electron
Raquel Alvarez Garcia (Geonium Chip group)
10 October 2023
Quantum illumination is a form of quantum-enhanced-metrology which presents several advantages over classical radar and near-field-imaging technologies. A practical implementation of the quantum illumination protocol in the MW domain is yet to be demonstrated, but a trapped electron in the "geonium" chip Penning trap proves the ideal candidate for a practical and deployable technology. This talk will introduce the quantum illumination protocol and discuss the changes and developments introduced to the "geonium" chip Penning trap in order to adapt the technology to the implementation of the protocol, including in the fabricated PCB chip, the electron loading mechanism and the planar magnetic field source.
Layering and Mesostructure Quantification on Freestanding Graphene Oxide Films by Wide Angle X-ray Scattering (WAXS)
Roque Sanchez Salas (Materials Physics group)
26 September 2023
Graphene oxide (GO) structure with several oxygen incorporated groups at the graphene network is well accepted as two-dimensional material regardless of their random out-of-plane oxygen atoms with a not-defined unit cell along its thickness of approximately 1 nm with intercalated water molecules along their layers.
This talk shows the effort towards the layering and mesostructure quantification of layered GO sheets inside the freestanding films. GO films were prepared by pouring and blade coating techniques and then characterized employing neutron X-ray scattering. The results show a methodology employing the alignment of the synchrotron X-ray beam and the layer GO sheets order on the poured and blade films. Moreover, the results suggest that GO sheets in dispersions can be reoriented by shear stress. We could propose an anisotropic ratio of GO sheets regarding the order of layering. Finally, the ratio of the studied GO films was contrasted in a short, medium, and long-range anisotropy based on their mesostructure morphology observed by polarized optical microscope.
Designing Robust Two-qubit Gate Schemes via Quantum Control 'Tricks'
Iason Apostolatos (Ion Quantum Technology group)
30 May 2023
Two-qubit gates are a much-coveted set of operations in the field of quantum computation. They are the critical ingredient which allows us to achieve entanglement, but they are also the hardest operations to execute. Performing two-qubit gates repeatedly with fidelities exceeding the fault-tolerant threshold (>99%) is a major challenge. This can be attributed to sensitivity to experimental noise, as well as miscalibrations of the gate’s many parameters. In our work, we identify two sources of noise that are detrimental to a gate’s performance: spin decoherence and motional decoherence. In this talk, we will be examining and summarising a set of quantum control techniques ('tricks') which can be applied in order to protect the two-qubit gate from the aforementioned sources of noise. This in turn leads to an improvement of the gate’s performance and an increase of its robustness to noise and miscalibration. However, introducing additional layers of protection and robustness to a two-qubit gate comes with an increased experimental overhead in the form of additional calibrations and additional costs to the available experimental hardware and software. This leads to a trade-off between the gate’s performance and its feasibility of being readily and quickly implemented.
Towards a Portable Single Ca+ ion Optical Clock
Vijay Singh (Ion Trap Cavity-QED and Molecular Physics group)
16 May 2023
Optical clocks are the most accurate measurement instruments to date. However, widespread use is being prevented by their large size, high cost and high technical complexity of operation. To overcome these obstacles, we are developing a compact, turn-key-operation portable optical clock based on trapped single Ca+ ions. The system is designed to fit in a 4-unit 19-inch module (50x52x16 cm), with a target weight under 20 kg and a target power consumption under 100 W. The targeted fractional frequency uncertainty of our system is ~10-16.
The key for the miniaturisation of the system is optical fibre integration, which provides not only compactness but also robustness. A fibre-based laser system provides all the necessary frequencies to ionise and laser-cool a Ca+ ion. The ion trap is an endcap style trap. Light is delivered to the ion via optical fibres and aspheric lenses inside the vacuum chamber. Fluorescence from the ion is collected using multimode fibres embedded inside the trap electrodes, offering a collection efficiency similar or even superior to traditional high NA lens approaches.
Combining this with the clean beam profiles offered by the delivery assemblies we can measure the presence of an ion with outstanding signal to background rations. The Ca+ quadrupole clock transition at 729 nm will be probed using a reference laser frequency stabilised to an ultra-stable optical cavity developed at NPL. Finally, on-board electronics controlling the various subsystems will run the system autonomously, making it a “black box” from the user’s perspective.
Exotic Electronic Properties of 2D Mica Nanosheets Produced by Liquid Phase Exfoliation
Cencen Wei (Materials Physics group)
2 May 2023
Phyllosilicate minerals such as mica family are generally considered as being spectrally inactive, electrically insulating, and chemically inert. Here, we demonstrate a method to obtain the aqueous suspensions of few-layer nanosheets by exfoliating the bulk mica in surfactant water solution to contradict the above. The quality of mica nanosheets was checked by employing the Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopies and electron diffraction. By using Raman spectroscopy, an interesting size and layer dependent property was observed. Through the UV-Visible spectroscopy, the high yield nanosheet suspensions of ~1 mg/mL was analysed and the bandgap narrowing from ~7 eV of the bulk to ~4 eV for in the single-layer sheets was obtained. Interestingly, the bandgap inversely scaled with nanosheet areal size, which was measured via Atomic Force Microscopy (AFM).
This unusual relationship originated from semiconducting behaviour is due to quantum confinement effects. Moreover, modelling X-ray diffraction (XRD) spectra reveals that lattice relaxation caused the initial bandgap decrease. Finally, mica few-layer nanosheets were proved that they have impressive catalytic abilities in hydrogen production process owing to their broad range of isomorphically substituted ions.
Mobile Total Field Optically Pumped Magnetometers for Navigation
Daniel Nightingale (Quantum Systems and Devices group)
18 April 2023
Global navigation satellite systems (GNSS) are at the forefront of navigation and are ubiquitous in everyday life. However, GNSS has limitations for use cases where satellite reception is limited (such as underground navigation). Dependence on the upkeep of existing satellite infrastructure, as well as the prevalence of jamming and spoofing devices limit the reliability of GNSS for the localisation of critical hardware. One alternative solution that does not suffer from these drawbacks is magnetic field navigation. This technique uses maps of local magnetic field anomalies and map-matching algorithms to determine position. We present a total-field Mx optically pumped magnetometer (OPM) system capable of operating within Earth's magnetic field. Battery operated control electronics allow for the OPM setup to be mounted on vehicles for the mapping of local magnetic fields. The pairing of this system with a conventional GNSS system will enable the evaluation of map-matching algorithms.
Cryogenic System for Characterization of Novel Quantum-Technologies
Pedro Taylor-Burdett (Ion Quantum Technology group)
4 April 2023
Impressive progress has been made in the field of quantum computing with trapped ions. In our group, we aim to build a ‘universal quantum computer’ capable of performing an arbitrary number of quantum algorithms, enabling problems to be solved that are classically intractable. However, progress towards this goal relies on the continual development of new quantum technologies, i.e. ‘the computer’s hardware’.
When it comes to in-vacuum technologies, such as new ion-trap designs or hardware for quantum control, characterisation and design-development can be an arduous and time-consuming process. This is, in part, due to the requirement for cleanroom-conditions and vacuum system ‘baking’ every time the vacuum-system is opened to modify the set-up. Generally, this process means weeks of down-time.
In this talk, I will be presenting the 4K cryogenic vacuum-system that has become the ‘testbed’ for many of our innovative technologies in the group. I will explain the advantages of using cryogenics and illustrate how we can achieve a 24h turn-over from one experimental set-up to the next.
Cavity Assisted Ion-Photon Entanglement
Ian Ford (Ion Trap Cavity-QED and Molecular Physics group)
21 March 2023
Trapped ions are a leading candidate in quantum networks. They benefit from long coherence times, and high fidelity state preparation and gate operations among other things. However the number of ions that can be well-controlled in any individual trap is very limited. To circumvent this, ions can be distributed among many smaller traps that are connected. Here the interaction of ions with single photons can be used to create these connections. In this way entanglement can be shared across traps allowing for more complex quantum algorithms. We couple calcium-40 ions trapped in a linear Paul trap to an optical cavity formed by two macroscopic mirrors to generate photons. By driving two separate Raman transitions simultaneously the ion state can be entangled to the polarisation state of the photon produced. By using a cavity to perform this ion-photon entanglement we aim to improve the rate of entanglement production that is possible.
Transfer-free in Situ Growth of Tunable Au-WSe2 Junctions
Sathvik Ajay Iyengar (Rice University, Texas)
7 March 2023
Two-dimensional transition metal dichalcogenides (TMDs) remain a topic of immense interest. Specifically, given their low operational switching costs, they find many niche applications in new computing architectures (eg: neuromorphic computing, hybrid CMOS) with the added promise of continued miniaturization. However, challenges lie in Back End of Line (BEOL) integration temperature and time compliance with regards to current requirements for crystal growth. Additionally, deleterious and time-consuming transfer processes and multiple steps involved in channel/contact engineering can cripple device performance.
Through a holistic approach, this work demonstrates kinetics-governed in-situ growth regimes (surface or edge growth from gold) of WSe2 and provides a mechanistic understanding of these regimes. As a proof-of-concept, we fabricate an in-situ device with flawless source-to-drain channel contacts, demonstrating a 2D semiconductor transistor via a “transfer-free” method within the 450-600 C 2h-time window requirement for Back End Of Line (BEOL) integration. We leverage directional edge growth to fabricate contacts with robust thickness-dependent junction tunability. Field effect transistor measurements reveal a low subthreshold swing of ~140 mV/decade, mobility of 107 ± 19 cm2V-1s-1, and robust ON/OFF ratios of ~106.
Automated Characterisation of Alkali Vapour-cells for Magnetometry
Leigh Thomas Page (Quantum Systems and Devices group)
21 February 2023
The sensitivity of optically pumped magnetometers have matched and even surpassed that of superconducting quantum interference devices (SQUIDs), with a number of advantages including its lack of required cryogenic cooling, increased portability and reduced maintenance costs. This has brought about an increase of interest in the technology. Applications in magnetic imaging, such as medical magnetoencephalography (MEG) or current density imaging in electric vehicle batteries, require many sensor channels to create detailed maps of magnetic fields. One crucial component in the sensor head is the atomic vapour cell. Such cells can be manufactured at large scales using standard silicon microfabrication techniques.
To analyse the quality of a large number of microfabricated cells, we developed a system consisting of an open source multipurpose 3-axis robot, mounted with a transmission spectroscopy setup, enabling the scanning of multiple cells in sequence via computer commands. The absorption lines in the scan can then be fit to linewidth broadening models, providing insight into the internal conditions of the cells. The automated quality analysis with our robotic system allows the calibration of manufacturing processes and selection of the vapour cells with desired parameters to be used in high-performance magnetometers.
Microfabricated Ion Trap Technology for Scalable Quantum Computing
Martin Siegele (Ion Quantum Technology group)
7 February 2023
A scalable system is fundamental for a large-scale quantum computer. For trapped-ion quantum computers, quantum charge-coupled devices (QCCD) are a promising approach. There are several challenges that need to be addressed. Shuttling ions between modules is one way to overcome device size limitations. Another major challenge for quantum computers is the scalable simultaneous execution of quantum gates. One approach to address this in trapped ion quantum computers is the implementation of quantum gates based on static magnetic field gradients and global microwave fields. A scalable system will require local ion loading on modules which can be achieved with integrated atomic ovens. I will discuss how to build microfabricated ion traps that allow these features for the demonstration of key technologies for scalable quantum computers in the IQT group.
A Ti:Sapph Laser System for the State-selective Photoionisation of Nitrogen
Amber Shepherd (Ion Trap Cavity-QED and Molecular Physics group)
24 January 2023
We are investigating possible time variations in the proton-to-electron mass ratio, which are predicted by some extensions to The Standard Model. For this, we will use high precision spectroscopy to probe a vibrational transition in nitrogen ions. In order to load nitrogen ions into the ion trap, we use a REMPI scheme to ionise nitrogen state-selectively into the ground state for the spectroscopy transition. However, the dye lasers used for this have a broad linewidth compared to the REMPI transitions. Therefore, seeded Ti:Sapph lasers with far narrower linewidths are being set up to improve the ionisation efficiency. Currently, both lasers have been set-up and characterised. Following this, frequency conversions will be implemented to produce the desired UV wavelengths of 212 nm and 253 nm.
Solution-processed Nanosheet Networks for Environmental Pollutant Sensing
Sean Ogilvie (Materials Physics group)
10 January 2023
Printed electronic devices facilitate widespread low-cost integration of interconnected sensors for applications including environmental monitoring. Challenges remain however because promising active materials for gas sensing are either synthetic or require elevated operating temperatures, both affecting cost and power consumption. Van der Waals nanomaterials such as graphene and molybdenum disulfide (MoS2) can be prepared from inexpensive naturally-abundant bulk powders using solution processing techniques into nanosheet networks. Semiconducting MoS2 networks exhibit promising electronic properties, but charge transport and sensing response remain limited by inter-nanosheet junctions.
Here, we study the electronic properties as a function of processing parameters including size and porosity and demonstrate design rules from enhanced conductivity. In turn, these optimised devices facilitate chemiresistive gas sensing where we demonstrate doping-sensitive and parts-per-billion sensitivity to important air pollutants such as nitrogen dioxide and ammonia, enabling applications in widespread sensor networks for public and environmental health.
- 2022 quantum talks
BEC Magnetic Microscopy
Shobita Bhumbra (Quantum Systems and Devices group)
29 November 2022
Cold atoms in the form of Bose-Einstein condensates (BECs) can be used to probe magnetic fields. This technique can be applied to indirectly measure electrical micro-currents within a sample. There are a wide range of applications for the sensing of micro-currents including: Silver nanowires used in flexible touchscreen technology, flexible electronics and stem cell differentiation facilitated by conductive carbon nanotubes. This talk will cover the BEC microscope concept and the progression of its development.
Trapped Ion Transport and Quantum State Control on Surface Electrode Traps Evolution
Sahra Ahmed Kulmiya (Ion Quantum Technology group)
15 November 2022
Trapped ion qubits achieve excellent coherence times and gate fidelities, well beyond the threshold for fault-tolerant quantum error correction. One of the routes towards scalability is the coherent control and transport of ions between different zones on a microfabricated surface trap. Ion transport operations should be as fast as possible to speed up quantum computation but must also preserve the motional quantum state. Through simulation of trapping potentials and ion dynamics, we can observe the effects of a transport protocol on the ions’ motional state and explore the transition from adiabatic to non-adiabatic evolution. We explore the optimisation of transport protocols using experiment and simulation.
A Flexible Ion Photon Interface for Quantum Computation
David Kay (Ion Trap Cavity-QED and Molecular Physics group)
25 October 2022
Optical cavities offer an avenue to scale up trapped ion-based quantum computers into a larger network. With an ion coupled to the cavity single photons can be efficiently generated, entanglement can be generated between the state of the ion and the emitted photon. To date, much work in this area generates entanglement between the ion state and the polarisation of the emitted photon. An alternative scheme, time bin entanglement, generates entanglement between the ion state and the time bin in which the photon was emitted. In this talk I will introduce time bin entanglement as our proposed scheme and how it compares to polarisation entanglement.
I will discuss the process by which photons are generated in an ion-cavity system and how the indistinguishability of the photon is measured. I will then provide an overview of the system we are currently developing; this will include a look at the femtosecond laser written, selectively-etched electrode chips which feature multiple trapping regions with the ability to shuttle ions through the trap into the dedicated cavity region. Details of the cavity mirrors will be provided including how they are fabricated and how the cavity module is integrated into the overall system.
Interconnecting Ion Trap Microchip Modules using Qubit Transport Operations
Foni Raphaël Lebrun (Ion Quantum Technology group)
14 June 2022
Recent efforts in trapped ion quantum computing have delivered impressive systems hosting up to 10s of qubits. However, to be able to solve broad and meaningful problems, practical quantum computers will require millions of such fully controlled qubits. To address this fundamental challenge, a quantum computer can be constructed following a modular approach. While this allows for far more modest qubit numbers per module, it also calls for the development of coherent links to distribute quantum information across a large-scale architecture.
To realise fault-tolerant quantum computation on such a platform, it is then key that inter-module interactions are realised at rates commensurate with quantum gate speeds. A significant step towards this goal has been the probabilistic distribution of entanglement between ion trap modules using optical interfaces. However, technological limitations currently hamper this photonic interconnect approach from reaching the desired effective connection rates. In this talk, an alternative method based on the inter-module transport of trapped ion qubits will be presented. This method relies on the engineering an electric field interface at the modules' edges, which creates a continuous confining potential that spans multiple modules.
I will discuss the experimental set-up that was constructed in the IQT group to investigate the feasibility of this technique. I will then discuss the realisation of quantum matter-links, i.e. inter-module qubit transfers, between two ion-trap microchips. To date, we have implemented such matter-links a rate of 2424 Hz, with a qubit transfer success probability in excess of 99.999993% and without measurable impact on the qubit state during transfer. Finally, I will detail our ongoing efforts to further increase the matter-link connection rates.
Optical Sensing of RF Performance Limits in Microfabricated Ion Traps
Scott Thomas (Ion Trap Cavity-QED and Molecular Physics group)
3 May 2022
High RF potentials are applied to traps to give tight confinement and long storage times. Low-noise performance is essential for performing coherent control of the ion qubits with high fidelities. The ability for the trap to operate under these RF potentials can be compromised by the presence of electronic breakdown. Even the faintest amount of breakdown can severely diminish the trapping efficiency. An RF testbed that has been developed to characterise the performance of newly fabricated microtraps is presented. Should any breakdown occur during testing it is detected optically. Image processing routines enhance the sensitivity of the measurement such that the onset of surface flashover type breakdown can be detected at amplitudes up to 90 V than is possible with unprocessed images.
A calibrated pickup measurement allows for the RF voltage amplitude on the trap to be determined without perturbing the resonant circuit that is used to apply the high voltages. These techniques will be used to improve the development of future devices. The principles demonstrated here also have applications beyond ion microtraps to other types of MEMS devices.
Graphene oxide (GO) structure with several oxygen incorporated groups at the graphene network is well accepted as two-dimensional material regardless of their random out-of-plane oxygen atoms with a not-defined unit cell along its thickness of approximately 1 nm with intercalated water molecules along their layers.
This talk shows the effort towards the layering and mesostructure quantification of layered GO sheets inside the freestanding films. GO films were prepared by pouring and blade coating techniques and then characterized employing neutron X-ray scattering. The results show a methodology employing the alignment of the synchrotron X-ray beam and the layer GO sheets order on the poured and blade films. Moreover, the results suggest that GO sheets in dispersions can be reoriented by shear stress. We could propose an anisotropic ratio of GO sheets regarding the order of layering. Finally, the ratio of the studied GO films was contrasted in a short, medium, and long-range anisotropy based on their mesostructure morphology observed by polarized optical microscope.
- 2021 quantum talks
Towards Multiple Bose-Einstein Condensates on an Atom Chip
Tasha Bierrum (Quantum Systems and Devices group)
7 December 2021
Through radio-frequency dressing, a Bose-Einstein condensate (BEC) can be coherently split in two creating a beam splitter style interferometer. This technique has been applied to study BEC properties1 and Josephson junctions. In this talk I will discuss how this can be extended with multiple radio-frequencies to coherently split a single BEC into three or more BECs, with the aim of investigating relative quantum phase 2. [1] Schumm, Matter-wave interferometry in a double well on an atom chip, Nature, p.57-62, 2005. [2] Leggett, Is ”relative quantum phase” transitive?, Found Phys, 25, 1, p.113-122, 1995.
Size-dependent Porosity Defines Conductivity in Liquid-exfoliated Nanosheet Networks
Hannah Wood (Materials Physics group)
23 November 2021
Transition metal dichalcogenides such as molybdenum disulfide (MoS2) are layered materials of great interest due to their interesting thickness-dependent properties and potential for optoelectronic devices. MoS2 can be prepared in dispersion by liquid phase exfoliation, size selected by liquid cascade centrifugation and deposited by vacuum filtration, spray deposition and printing techniques. Here, the dependence of the electrical conductivity of MoS2 nanosheet networks on the average lateral size is investigated. Size-selected dispersions are characterised by statistical atomic force microscopy and UV-visible extinction spectroscopy using established metrics.
We find that network conductivity increases as nanosheet size decreases, suggesting that nanosheet packing dominates over the increasing density of inter-nanosheet junctions. The conductivity in the networks of the smallest nanosheets reaches 10-3S/m, a thousandfold increase on that of the larger nanosheets reported in the literature. This conductivity enhancement is understood in terms of nanosheet packing and porosity, enabling their development towards applications in printed optoelectronic devices.
Laser Cooling of Antihydrogen
Graham Stutter (Ion Trap Cavity-QED and Molecular Physics group)
9 November 2021
Performing precision laser spectroscopy on the 1S-2S transition in antihydrogen is a long-standing goal of the antimatter community and a common aim of many of the experiments based in the Antiproton Decelerator (AD) facility at CERN. Comparing this frequency to the equivalent transition in hydrogen – which has been measured to a precision of a few parts in 1015 – provides a direct test of CPT theorem, which dictates that the spectra of hydrogen and antihydrogen must be identical.
In 2017, the ALPHA collaboration performed detailed spectroscopy of the 1S-2S transition in antihydrogen for the first time and found agreement with the expected hydrogen transition to a relative precision of 2x10-12. These measurements were limited by transit time broadening, a result of the velocity of antihydrogen in our magnetic minimum trap. To reduce this velocity, we have pursued Doppler cooling on the Lyman-α transition at 121nm. In this talk I will present results from these efforts and their effect on our observed 1S-2S lineshape.
Full-wave Control of Ultrafast THz Pulses in Complex Media
Vittorio Cecconi (Emergent Photonics Laboratory)
26 October 2021
We present a theoretical investigation of broadband, spatiotemporal control of terahertz light in random media based on the nonlinear conversion of spatially modulated ultrashort pulses and time-domain field detection.
Robust Entanglement of Trapped Ions with an Indirect Spin-Spin Interaction
Christophe Valahu (Ion Quantum Technology group)
12 October 2021
Trapped ions placed in a static magnetic field gradient are subject to a spin-dependent force. Interestingly, this force allows the spins of two ions to couple to one another. This can be used as the basis for an entangling two-qubit gate, however the spins are very susceptible to magnetic field noise which limits the gate's fidelity.
We show how to combine the spin-spin coupling interaction with dressed states, a decoherence free subspace that mitigates the effects of magnetic field noise. The resulting entangling gate is very robust to motional decoherence, which strongly alleviates experimental complexities.
Magnetocephalography using Optically Pumped Magnetometers (OPMs)
Aikaterini Gialopsou (Quantum Systems and Devices group)
28 September 2021
Magnetoencephalography (MEG) is a widely used neuroimaging technique with numerous clinical applications. Technological developments with Optically Pumped Magnetometers (OPMs) has enabled new non-invasive brain function mapping capabilities with OPM-MEG, offering improved sensor placement flexibility, and closer positioning to the scalp, compared to superconducting quantum interference devices (SQUIDs). OPMs also offer an improved spatial resolution with increased source localisation. Here we provide a detailed explanation of the OPM MEG application and the significant advantages over the SQUID MEG in neuroscience.
Tuneable Synthetic Reduced Graphene Oxide Scaffolds Elicit High Levels of Three-dimensional Glioblastama Interconnectivity in Vitro
Chris Brown (Materials Physics group)
14 September 2021
Three-dimensional tissue scaffolds have utilised nanomaterials to great effect over the last decade. In particular, scaffold design has evolved to consider mechanical structure, morphology, chemistry, electrical properties, and of course biocompatibility – all vital to the performance of the scaffold and how successful they are in developing cell cultures. We have developed an entirely synthetic and tuneable three-dimensional scaffold of reduced graphene oxide (rGO) that shows good biocompatibility, and favourable mechanical properties as well as reasonable electrical conductivity. Importantly, the synthesis is scaleable and suitable for producing scaffolds of any desired geometry and size, and we observe a high level of biocompatibility and cell proliferation for multiple cell lines. In particular, one of the most devastating forms of malignant brain cancer, glioblastoma (GBM), grows especially well on our rGO scaffold in vitro, and without the addition of response-specific growth factors.
We have observed that our scaffold elicits spontaneous formation of a high degree of intercellular connections across the GBM culture. This phenomenon is not well documented in vitro ;and nothing similar has been observed in synthetic scaffolds without the use of response-specific growth factors – which risk obscuring any potential phenotypic behaviour of the cells. The use of scaffolds like ours, which are not subject to the limitations of existing two-dimensional substrate technologies, provide an excellent system for further investigation into the mechanisms behind the rapid proliferation and success of cancers like GBM. These synthetic scaffolds can advance our understanding of these malignancies in the pursuit of improved theranostics against them, whilst also reducing the current reliance on animal testing.
Towards High Resolution Spectroscopy of Molecular Nitrogen Ions
Laura Blackburn (Ion Trap Cavity-QED and Molecular Physics group)
20 July 2021
High resolution spectroscopy of molecules is a prime candidate to measure potential temporal changes in the proton-to-electron mass ratio, μ. By measuring a vibrational transition within a molecule with unparalleled precision and comparing it to an optical atomic transition, potential changes in μ can be detected. In our experiment we use N2+ , which has systematic shifts even better than the currently best optical atomic clocks. To perform precision spectroscopy, a single 14N2+ ion will be co-trapped, in a linear Paul trap, with a 40Ca+ ion which will act as a frequency reference and be used for the cooling and state detection of the nitrogen ion. A vibrational Raman transition in the nitrogen ion will be compared to a quadrupole transition in the calcium ion.
Prerequisite to this is the preparation of 14N2+ in a specific rovibronic state. Recently, a 2+1’ resonance-enhanced multiphoton ionisation (REMPI) scheme was developed, using the a1Σg+(ν=6) ← X1 Σg+ (ν=0) band in 14N2 for the resonant excitation. This scheme demonstrated a fidelity of >99% for loading into the rovibronic ground state. Simulations indicate that the high amplitude and inhomogeneous electric fields of the ion trap will broaden the ionisation threshold and prevent state-selective loading in many cases. Rapidly switching the trap off during loading can reduce the broadening and may mitigate the broadening.
Video Rate Terahertz Near-Field Hot Carrier Microscopy
Robyn Tucker (Emergent Photonics Laboratory)
6 July 2021
Semiconductor composite devices, structured materials, and metasurfaces require intricate knowledge of ultrafast carrier dynamics to characterise their physical mechanisms. Because Terahertz (THz) radiation interacts classically with free carriers, material physics widely utilises THz time-domain spectroscopy coupled with a photo-exciting pump to cause photon absorption of carriers so that relaxation, recombination, and other complex processes can be observed with optical probing. Unfortunately the coarse THz diffraction limit restricts the resolution of the retrieved spatial morphology distribution in non-uniform media; even well-established point-scan methodologies are extremely slow and fail to resolve non-local interactions between regions of a 2D sample.
This talk proposes and presents the implementation and results of a novel nonlinear, fully parallel and wide-area near field methodology, known as Optical-Pump Terahertz Near Field Microscopy (OP-TNFM). This methodology enables the mapping of hot carrier distributions on material surfaces and their characteristic dynamics with resolutions exceeding the THz diffraction limit. OP-TNFM allows for the wide-area assessment of heterogeneous systems with arbitrary excitation distributions while simultaneously providing the ultrafast time-domain evolution of THz field.
Around the Bend: Linking 1D Planar Ion Traps in a 2D Array
Alex Owens (Ion Quantum Technology group)
22 June 2021
Linear RF ion traps have been employed to great effect intermediate scale quantum computing experiments, as they provide excellent isolation of small quantum systems from the decohering effects of the outside world. To tackle large scale computing problems with ions will require distribution of information over an array of traps, though the isolation ion traps provide makes coupling them together somewhat tricky.
We approach this coupling issue by physically shuttling ions between linear traps through ‘X-junctions’ where the RF electrodes of 4 linear traps meet. I will be talking about design considerations for traps with junctions, what makes a good or bad ion trajectory and approaches to modelling the problem along with some discussion of experimental results/bumps in the road!
Coherence Properties of Bose Gases with Tuneable Dimensionalities
Rob Shah (Quantum Systems and Devices group)
8 June 2021
Bose-Einstein condensation (BEC) is a quantum many-body phenomenon that is most typically realised by cooling a gas of alkali atoms down to ultracold temperatures, usually a few hundred nano-Kelvin. A stand-out feature of a BEC is it’s fully coherent nature, and they are often labelled as the matter-wave equivalent to a laser beam.
This presentation describes how we produce BECs in the laboratory, and how experimentally we can manipulate the gas’ confining potential to control the dimensionality. Interestingly, as the dimensionality is reduced there is also a loss in phase coherence which we observe during imaging as the formation of an interference pattern within the atomic density, these gases are known as quasi-condensates. The coherence properties of BECs and quasi-condensates are then discussed with support from our experimental investigation.
Size-Dependent Conductivity in Graphene Networks Enables Thermoelectric Applications
Keiran Clifford (Materials Physics group)
25 May 2021
Graphene is the most well-known and comprehensively studied two-dimensional layered material, with a remarkable and unique combination of electrical, mechanical, and thermal properties. Liquid-phase exfoliation (LPE) techniques facilitate the production of pristine graphene on a large scale at relatively low-cost. Size selection of these LPE dispersions, followed by a thermal annealing step, results in the highest reported value of electrical conductivity (1.2 x 105 S m-1) of any solution-processed graphene to date, enabling applications in printed electronics and energy storage devices.
Recent work on this material’s thermoelectric performance indicates that it shows promise as a low-cost, green material for thermal energy harvesting applications.
Towards Ion-photon Entanglement in the Strong Coupling Regime Within a Fibre-based Fabry-Perot Cavity
Corentin Pignot (Ion Trap Cavity-QED and Molecular Physics group)
11 May 2021
Ions and photons are some of the most promising qubits to create a quantum network. They give the possibility to create and transfer information at the quantum level. Quantum applications such as quantum key distribution or quantum computing rely on efficient entanglement processes between qubits.
In this talk, I will present one scheme to entangle a single calcium 40 ion with a single photon within an optical fibre cavity operating in the strong coupling regime. I will also present a way to measure the fidelity of the process with the use of a second mapping photon. This scheme is being implemented in one of our ion traps and some preliminary results will be shown.
Seeing Through Scattering
Vivek Kumar (Emergent Photonics Laboratory)
27 April 2021
Scattering of light is critical to many applications such as deep tissue biological imaging, laser surgery, geophysics and Lidar based applications. However, light scattering prevents focusing beyond a certain depth inside the medium which limits all these applications to shallow depths, so it is highly desired to break this diffusion limit and focus light deep inside the medium. In this talk, I will present spatiotemporal refocusing of THz waves following a direct measurement of propagation properties of the scattering medium.
Towards Improving Quantum Coherence - In-situ RF Microplasmas with Energies suited to In Situ Selective Cleaning of Surface Adsorbates in Ion Microtraps
Dr Mariam Akhtar (Ion Quantum Technology group)
13 April 2021
The coherent control of trapped ions has many applications in quantum technologies from quantum information processing to quantum metrology and optical atomic clocks. However, motional decoherence due to electric field noise remains a limiting factor. A dominant source of noise is thought to be caused by surface adsorbates. The use of in-situ RF microdischarges has the potential to selectively sputter contamination.
This work demonstrates a capacitively-coupled, radio-frequency (RF) microplasma inside the 3D electrode structure of an ion microtrap device. Spectroscopic analysis of the He I 667 nm and Hα 656 nm emission lines yielded the gas temperature and electron density, which enabled calculation of the mean ion bombardment energy. For He sputtering of hydrocarbon adsorbates on Au, we calculate that the high energy tail of the distribution should remove adsorbate monolayers in as little as 1 min of processing. We also calculate that the distribution is insufficiently energetic to have any significant effect on the Au electrode surface within that duration. Our results suggest that the microplasma technique is suited to in situ selective removal of surface adsorbates from ion microtrap electrodes.
Spin-Exchange-Relaxation-Free Optically Pumped Magnetometers and their Application
Thomas Coussens (Quantum Systems and Devices group)
30 March 2021
Since the 1960s, SQUIDs have been the benchmark for sensitive magnetic field measurement. However, developments in the Spin-Exchange-Relaxation-Free (SERF) optically pumped magnetometers (OPMs) has allowed for similar, if not better sensitivity compared to SQUIDs, as well as a number of additional advantages.One particular benefit of OPMs is the reduced distance from a magnetic source to the sensor, which is of particular interest for magnetoencephalography (MEG), where OPMs are able to offer improved spatial resolution than previously possible.
This talk will outline the principles of SERF magnetometry and discusses the potential benefits in both industry and medical settings, including the monitoring of currents within electric vehicle batteries.
Regulating Graphene Wrinkles in the Vertically Stacked Hybrid Structure
Dr Manoj Tripathi (Materials Physics group)
16 March 2021
The artificial stacking of (2D) heterostructure brings remarkable applications of tuned physical, electrical and optical properties. The van der Waals interaction at heterointerface can generate desirable physics of nanomaterials that leads to the emerging field interface engineering. Some of the crucial contributions of hetero-layer devices are processed by regulating strain and doping at the interface by fabricating structural disorders at the nanoscale. Nevertheless, a critical understanding of nanoscale mechanics and interfacial vdW interaction is required to fabricate the desired architecture.
In the present work, I will demonstrate the tuning of interfacial interaction between graphene-MoS2 heterostructure for enhancing the geometry of graphene wrinkles. I will discuss the role of generated strain at the interfacial region regulates shear force which is responsible for the sliding of the top layer on a solid-state lubricant, MoS2. The present work clearly shows the beginning of an era constructing nanoscopic structures by regulating fundamental forces.
- 2019 quantum talks
Single Microwave Photon Detection
Ryan Willets (Geonium Chip group)
2 April 2019
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.
The Two Colour Magneto Optical Trap
Tim James (Quantum Systems and Devices group)
26 March 2019
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.
Complexity-driven Photonics: Collective Interactions and Spontaneous Synchronisation in Nonlinear Photonic Systems
Juan Sebastian Totero Gongero (Emergent Photonics Laboratory)
5 March 2019
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.
Microfabrication of Surface Ion Trap Chips
Seokjun Hong (Ion Quantum Technology group)
26 February 2019
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.
Quantum Sensing using Trapped Ions
Harry Bostock (Ion Quantum Technology group)
5 February 2019
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.
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