Use cases, challenges and protocols (continued)

Entanglement creation using parametric down-conversion (PDC) sources has enabled pioneering studies of foundational physics and proof-of-principle demonstrations of quantum information processing techniques. However, typical PDC sources produce unwanted spectral correlations which degrade two-photon interference, introducing errors in the generation of multi-photon states.

Employing domain-engineering techniques to directly modify the non-linear PDC process to significantly suppress unwanted spectral correlation, we remove the need for spectral filtering. With this same technique, we have also demonstrated time-frequency mode entanglement and time-frequency hyper-entanglement.

For the generation of pure telecom photons, the optimisation of parameters that trade-off the non-trivial relationship between non-linearity and indistinguishability enabled us to improve upon previous crystal designs to operate on the achievable limits of domain-engineered PDC. We experimentally measured two-photon interference visibilities of up to 98.6 ± 1.1% between photons generated from two independent sources without filters. As a result, we obtain net heralding efficiencies up to 67.5%, corresponding to overall collection efficiencies exceeding 90%.

With the performance figures presented here, we can produce complex photonic graph states with high rates, allowing for experiments addressing realistic challenges prominent within prospective long-distance quantum networks.

Optimised parametric down-conversion sources for generating telecom graph states

Quantum measurements lie at the heart of experimental quantum science and quantum information processing. Traditionally, these measurements take the form of projecting a state intoa certain basis which tells us information about what the state is. Quantum state elimination (QSE) has recently garnered attention as an alternative approach where the outcomes tells uswhat the state is not. QSE plays a role in foundational physics about what is the nature ofa quantum state established by Pusey, Barrett and Rudolph (PBR). Recently, J. Crickmore, etal (Phys. Rev. Res., 2, 013256) proposed a new protocol for two-out-of-four state elimination extending QSE to a multiqubit setting. Specifically, the authors introduced a non-trivial set off our states that cannot be resolved by projective measurements on each qubit, instead requiring entangled measurement operators. These entangled measurements take the form of POVMs. States are encoded into pathmodes while the POVM is implemented interferometrically. We employ a beam displacer type interferometry for passive path mode stability. Specific detection events correspond to a POVM element which, along with a certain prepared state, results in two-out-of-four states being eliminated. Beyond being a proof of principle demonstration, useful quantum communication andcryptography schemes will be investigated.

Experimental realisation of 2 out of 4 quantum state elimination

A single quantum measurement cannot perfectly determine the state of a quantum system; however it is possible to perfectly rule out certain states. Quantum state elimination is of foundational interest, relating to the so-called reality of the wave function, as well as having applications in quantum information and quantum communication. We consider unambiguous quantum state elimination for two qubits, where each qubit can be in one of two possible states resulting in four possible two-qubit states. We provide an optimal measurement for eliminating two states out of four two-qubit states. We also explore different possible optical realisations of this state elimination measurement using linear optics and generate a realization that uses a minimum number of optical elements. This state elimination measurement could be used for an XOR oblivious transfer protocol, where a receiver obtains either the first, second, or XOR of two bits a sender sends and the sender not knowing which bit was received. Moreover, one could also envisage a novel quantum key distribution schemes employing state elimination, where the final bit value cannot be thought of as created at the sender and transmitted to the receiver, but is only realised once the receiver's measurement is complete.

Unambiguous quantum state elimination of pairs of quantum states for quantum communication

**Session Chair:** Reza Nejabati, University of Bristol, UK


 **Alessandro Fedrizzi,** Heriot-Watt University, UK 
 Title of talk: Graph State Quantum Networking


 **Martin Suchara**, Argonne National Laboratory, USA
 Title of talk: Quantum Network Simulations - Towards Reliable, Scalable, and Secure Quantum Network Architectures


 **Adrian Wonfor**, University of Cambridge, UK
 Title of talk: UK Quantum Networks


 **Sebastian Neumann**, IQOQI-Vienna, Austria
 Title of talk: QUAPITAL: In-fibre quantum key distribution crossing borders


 **Closing remarks: 
 John Rarity**, University of Bristol, UK

Session 3: Use cases, challenges and protocols (continued)

technical paper

[![](https://assets.underline.io/uploads/markdown_image/1/image/cbbd5f12758de05fc454b48dffd0987f.png)](https://twitter.com/QCommHub)

This Workshop aims to bring together researchers from UK’s Quantum Communication Hub programme and similar initiatives across the world to discuss technological challenges and solutions for creating the next generation of quantum communication networks featuring enhanced operational capabilities to address the requirements for a variety of applications and use cases including quantum key distribution, quantum internet, blind and distributed quantum computing.

### Our speakers and title of talks:

 **Eleni Diamanti**, Trusted and Untrusted Node QKD Networks Leveraging Telecom Technology, Pierre and Marie Curie University & Paris Centre for Quantum Computing, France
 **Sebastian Etcheverry**, CV-QKD driven by QRNG for deployment of secure communication, The Institute of Photonic Sciences (ICFO), Spain
 **Alessandro Fedrizzi,** Graph state quantum networking, Heriot-Watt University, UK
 **Hannes Hübel**, Field trial of QKD-secured Secret Sharing, Austrian Institute of Technology, Austria
 **Siddarth Koduru Joshi**, Entanglement based quantum networking, University of Bristol, UK
 **George Kanellos,** Fully Autonomous Dynamic Quantum Networking, University of Bristol, UK
 **Marc Kaplan**, Applications of quantum networks: the short and the long term, VeriQloud, France
 **Elham Kashefi**, Privacy and Security in Quantum Network, University of Edinburgh, UK and CNRS Sorbonne University, France
 **Jake Kennard**, Chip based QKD, KETS Quantum, UK
 **Navin Lingaraju**, Spectral multiplexing and information processing for quantum networks, Purdue University, USA
 **Andrew Lord,** QKD: Evolution from point-point customer solutions to national networks, BT Group, UK
 **Norbert Lütkenhaus**, QKD as performance metric for Quantum networks, University of Waterloo, Canada
 **Roger McKinlay**, *Session Chair*, Innovate UK
 **William Munro**, Architecturing robust quantum networks, NTT Basic Research Lab, Japan
 **Reza Nejabati**, *Session Chair*, University of Bristol
 **Sebastian Neumann**, QUAPITAL: In-fibre quantum key distribution crossing borders, IQOQI-Vienna, Austria
 **Richard Penty**, *Session Chair*, University of Cambridge
 **Stefano Pirandola**, Optimal Quantum Communications, University of York (Quantum Communications Hub), UK
 **John Rarity**, *Closing Remarks*, University of Bristol
 **Andrew Shields**, Extending the performance of quantum key distribution, Toshiba Europe Ltd., UK
 **Tim Spiller**, *Opening Remarks*, University of York
 **Martin Suchara**, Quantum Network Simulations - Towards Reliable, Scalable, and Secure Quantum Network Architectures, Argonne National Laboratory, USA
 **Stephanie Wehner**, Towards a Blueprint for a Quantum Internet, QuTech, TU Delft, Netherlands
 **Adrian Wonfor**, UK Quantum Networks, University of Cambridge, UK
 **Qiang Zhang**, Recent experimental progress in quantum network in China, University of Science and Technology of China, China

<iframe width=1280 height=720 frameborder="0" scrolling="no" src="https://screencast-o-matic.com/player/crfYDhVnW89?width=1280&height=720&ff=1&title=0&controls=1?start=1" allowfullscreen="true"></iframe>

Next Generation Quantum Networking Workshop 2021

Poster session 1 & networking on Gathertown

poster

**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

QC-1: Quantum Communication

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 2020

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. 

Alessandro Fedrizzi

4

SHORT BIO

Presentations

Use cases, challenges and protocols (continued)

Optimised parametric down-conversion sources for generating telecom graph states

Experimental realisation of 2 out of 4 quantum state elimination

Unambiguous quantum state elimination of pairs of quantum states for quantum communication

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