China

Global scale quantum communication links will form the backbone of the quantum internet. However, exponential loss in optical fibres precludes any realistic application beyond few hundred kilometres. Quantum repeaters (QR) and space-based systems offer to overcome this limitation. However, the most ambitious land based QR architecture is limited to around 4000 km beyond which meaningful secret generation becomes impossible. On the other hand, majority of the satellite-based quantum communication architectures proposed so far are either limited to the line-of-sight distance of the orbit or they rely on satellites as trusted nodes. Here, we analyse the use of quantum memory (QM)-equipped satellites for quantum communication focussing on global range repeaters and Measurement-Device-Independent (MDI) QKD. We show that a network consisting of satellites equipped with QMs could offer orders of magnitude faster entanglement distribution rates across the whole globe than the existing hybrid, space-ground protocols. We further analyse how entanglement distribution performance depends on memory characteristics, determine benchmarks to assess performance of different tasks, and propose various architectures for light-matter interfaces. Our work provides a practical roadmap to realise unconditionally secure quantum communications over global distances with current technologies.



Quantum 2020

Space-borne quantum memories for global quantum communication

space-based qkd

quantum memories

quantum networking

quantum communication

**BQIT is a three day annual workshop** aimed at enabling leading UK and international academics and industrial partners to come together; to explore and discuss future ambitions and challenges in the field of **Quantum Information Technologies.** Since our conception in 2014 we have had 230 speakers and panellists who have presented their work and opinions on a range of topics, from quantum theory to innovation in industry.


### Welcome Message
The BQIT:21 team welcomes you to the eighth Bristol Quantum Information Technologies workshop! 

Last year was the first time in our workshop's history that we had gone fully virtual. The global circumstances that continue to impact us all professionally and personally have forced BQIT once again to be delivered as an all-virtual workshop for 2021. The access this creates to colleagues across the world who would otherwise be unable to join us, as well as being able to make the workshop free for all attendees due to the lower costs involved in delivering an online workshop, are just a couple of the extraordinary benefits of meeting online. This also means that we can welcome three times as many attendees to BQIT than previous years.   

We take this opportunity to thank each of our speakers and poster presenters for contributing their technical content, this year's sponsors, whose support this year enabled BQIT:21 to be free to all attendees, and to all of our attendees for joining us online this year. We recognise the extra energy required to stay connected and motivated during these difficult times, and are hugely encouraged to see so many of you willing to continue to connect with us on an online platform. 

It is our hope that you have a productive and enjoyable time while you engage and interact with BQIT:21, and to everyone that has helped take BQIT:21 online, thank you! 

**The BQIT board and organisation team **


![](https://assets.underline.io/uploads/markdown_image/1/image/a12e0c1ad3410144cb48557690e4ecaf.png)
### This year's workshop agenda is available here: [Virtual BQIT:21](https://drive.google.com/file/d/1QwsSM0ztnxC_lgUKf3TbO3GvnI44AQkY/view?usp=sharing)
For further information, please contact us at: **bqit-admin@bristol.ac.uk**

![](https://assets.underline.io/uploads/markdown_image/1/image/a12e0c1ad3410144cb48557690e4ecaf.png)

Bristol Quantum Information Technologies Workshop

technical paper

The Institute of Physics and IOP Publishing, in partnership with the Chinese Physical Society (CPS) and the University of Science and Technology of China (USTC) are proud to have brought together the international quantum science community online for this inaugural conference.


Early career and leading researchers from universities, industry and government worldwide came together to share, learn and collaborate on the latest research and emerging areas of high interest across quantum science and technology. The broad themes covered by Quantum 2020 included:

Quantum communication;
Quantum computing and quantum simulation;
Quantum sensing, metrology and imaging;
Quantum information theory, software and algorithms;
Quantum foundations;
Quantum technology in industry.
The four-day event featured talks from world-renowned scientists, interactive poster sessions and two exciting panel discussions on the themes of Quantum Technology in Industry and Quantum Technology Programmes Around the World.


You will need to [register](https://www.iopconferences.org/iop/frontend/reg/tRegisterEmailNew.csp?pageID=978403&eventID=1552&tempPersonID=536224) to obtain a ticket. . If you have already registered you should have been sent an email from Underline (to the email address that you registered with) with the subject line ‘Welcome to Quantum 2020’. This email includes your ticket for the event. 

If you have a ticket and are experiencing problems in accessing the event, please contact us. 

Quantum computers are expected to offer speed-ups for solving certain scientific problems. One example is digital quantum simulation, where sequences of quantum gates can be used to simulate the dynamics of quantum systems in polynomial time. This could have applications in simulations of quantum optimal control, which aim to identify shaped fields to drive a quantum system towards a designated control objective. In this talk, I will explore how digital quantum simulation could be used to make quantum optimal control simulations more tractable. I will introduce a framework that utilizes a quantum computer to simulate the field-induced dynamics of a quantum system in combination with classical optimization to update the field. As a demonstration of this framework, a series of numerical illustrations involving quantum molecular control problems will be presented.

Sandia National Labs is managed and operated by NTESS under DOE NNSA contract DE-NA0003525

Digital quantum simulation of molecular dynamics and control

Materials for Quantum Technology (MQT) is a new multidisciplinary, open access journal from IOP Publishing devoted to publishing cutting-edge research on the development and application of materials for all quantum-enabled technologies and devices.


Materials for Quantum Technology - a new multidisciplinary journal from IOP Publishing

Over the last few years, IOP Publishing has been building a library of cutting-edge books for the scientific community. This includes the area of quantum science and technology, especially through the IOP Series in Quantum Technology. Taking advantage of the capabilities of electronic publishing and capitalizing on the enhanced features modern ebooks allow, we have created an award-winning programme, designed to both enhance the reader experience and deliver a service to suit the need of modern libraries and readership models. Features that are especially important in this time of increased online and distance learning

(IOPP) IOP ebooks, a New Paradigm in Book Publishing

A multidisciplinary, high impact journal devoted to publishing research of the highest quality and significance covering the science and application of all quantum-enabled technologies.

Quantum Science and Technology - IOP Publishing's leading journal dedicated to quantum science

Launched in 1998, New Journal of Physics (NJP) is a broad scope, open access journal, owned by the German Physical Society (DPG) and the Institute of Physics, UK. NJP's core mission is to make accessible to its broad physics readership the most significant topics across all of physics. The breadth of its coverage makes it particularly well-suited to showcasing interdisciplinary topics. 

NJP is committed to innovation in publishing, offering all authors a variety of novel features, including double-blind peer review, video abstracts, and interactive figures. NJP showcases leading research through a variety of article types, including Topical Reviews and Perspectives. The long-standing and prestigious Focus Issue series highlights key emerging topics by inviting articles from the leading specialised researchers across the world.

As an open access journal, NJP articles have outstandingly high visibility - every paper is downloaded hundreds of times within weeks of publication - and article publication charge discounts are available for many societies/institutions, including the Chinese Academy of Sciences, the DPG and the IOP.

With its broad scope and focus on publishing free-to-read, high-quality research, NJP is the ideal venue for authors seeking to promote their outstanding research to the wider physics community.

New Journal of Physics - the open access journal at the forefront of physics

Superconducting qubits are a subject of intense research as a platform for scalable quantum computing. While transmon qubits have received a lot of attention, the less ubiquitous Fluxonium qubit has been shown to have long life-times and gates unlimited by level anharmonicity [1-2]. Despite this, little research has been put into studying multi-Fluxonium devices. Here, one of the difficulties is understanding how their rich level structure can make them prone to measurement photons inducing transitions out of the qubit subspace [3]. We present a systematic study of a system comprising two capacitively coupled Fluxonium qubits sharing the same read-out cavity. By tracking the state dependent transmission of the read-out pulse, we determine the transition rates Γij from state i to state j of the coupled system using a forward-backward analysis [4] to characterise these cavity induced transitions. By varying the flux bias of the system and the population of the cavity, we characterise the fidelity of this read-out.

[1] L.B. Nguyen et al., Phys. Rev. X 9 041041, 2019
[2] H. Zhang et al., arXiv:2002.10653, 2020
[3] D. Sank et al., Phys. Rev. Lett. 117 190503, 2016
[4] T. Rybarczyk et al., Physical Review A 91 062116, 2015


Cavity Induced State Transitions in a Coupled Fluxonium Qubit System

Machine Learning has wide applications in a broad range of subjects, including physics. Recent works have shown that neural networks can learn classical Hamiltonian mechanics. The results of these works motivate the following question: Can we endow neural networks with inductive biases coming from quantum mechanics and provide insights for quantum phenomena? In this work, we try answering these questions by investigating possible approximations for reconstructing the Hamiltonian of a quantum system given one of its wave–functions. Instead of handcrafting the Hamiltonian and a solution of the Schrödinger equation, we design neural networks that aim to learn it directly from our observations. We show that our method, termed Quantum Potential Neural Networks (QPNN), can learn potentials in an unsupervised manner with remarkable accuracy for a wide range of quantum systems, such as the quantum harmonic oscillator, particle in a box perturbed by an external potential, hydrogen atom, Pöschl–Teller potential, and a solitary wave system. Furthermore, in the case of a particle perturbed by an external force, we also learn the perturbed wave function in a joint end-to-end manner.

Learning Potentials of Quantum Systems Using Deep Neural Networks

This poster details some of the current initiatives at IOP Publishing (IOPP) aimed at improving the author and reviewer experience.

Our research suggests there are deficiencies in the peer review process, specifically linked to equality, diversity, transparency, quality and training. This is supported by academic literature on publishing and higher education. Many of these themes are the result of multiple historical and systemic issues.

In recent months IOPP have announced a mix of new and updated initiatives aimed at addressing some of these complex challenges. These include changes to the peer review workflow, the creation of a unique training programme, and publication of peer review reports with published articles.


Evolving Peer Review at IOPP: Diversity, Training and Transparency

Photonic graph states are underlying resources for one-way optical quantum computation, quantum error correction, fundamental testing of quantum mechanics, and quantum communication networks. Most existing works, however, are based on the spontaneous parametric down-conversion sources that intrinsically suffer from probabilistic generation and double pair components. Here, we create two important classes of graph states, a polarization-encoded four-photon Greenberger−Horne−Zeilinger (GHZ) state and a linear cluster state, by actively demultiplexing a deterministic single photon source from a semiconductor quantum dot embedded in a micropillar. A state fidelity of 0.790 ± 0.009 (0.763 ± 0.004) and a count rate of ~13Hz are observed for the four-photon GHZ (cluster) state. The results constitute a new route toward the multiphoton entanglement with deterministic single-photon sources.

Multiphoton Graph States from a Solid-State Single-Photon Source

Realizing strongly-correlated topological phases of ultracold gases is a central goal for ongoing experiments. And while fractional quantum Hall states could soon be implemented in small atomic ensembles, detecting their signatures in few-particle settings remains a fundamental challenge. In this work, we numerically analyze the center-of-mass Hall drift of a small ensemble of hardcore bosons, initially prepared in the ground state of the Harper-Hofstadter-Hubbard model. By extracting the Hall conductivity in a wide range of the magnetic flux, we identify an emergent Hall plateau compatible with a fractional Chern insulator state: the width of the plateau agrees with the spectral and topological properties of the prepared ground state, while the Hall conductivity approaches a fractional value determined by the many-body Chern number. A comparison with a direct application of Streda’s formula is also discussed. Our calculations suggest that fractional Chern insulators can be detected in cold-atom experiments, using available detection methods.

Ref: C. Repellin, J. Léonard, and N. Goldman, arXiv:2005.09689.

Space-borne quantum memories for global quantum communication

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Digital quantum simulation of molecular dynamics and control

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