China

The effect of photon-pair generation rate on quantum entanglement is analyzed.
Two techniques of producing polarization entanglement are compared: a continuously pumped spontaneous parametric down-conversion (SPDC) and a biexciton decay in a quantum dot. We made a comparison of the reconstructed entangled states in terms of performance under device-independent quantum key distribution. We found that the secure key rate of down-converted photon pairs is limited to 0.029 bits per detection window due to intrinsic multiphoton contributions. We also report that there exists one optimum gain for continuous-wave down-conversion sources. We find a bound for secure key rate extracted from SPDC sources and show that quantum dot sources can surpass them with future advancement of their capabilities.


Quantum 2020

Effect of source statistics on utilizing photon
entanglement in quantum key distribution

quantum entanglement

quantum communication

spontaneous parametric down-conversion

quantum key distribution

**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

poster

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. 

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. 

Long-lived quantum coherences detected in the Fenna-Matthews-Olson (FMO) light-harvesting complex have ignited the hunt for realistic models that can explain such dynamics. The extraordinary ~100% efficiencies presented by these complexes, operating under noisy environmental conditions, make them an important target for understanding and replicating their success in other practical applications. Despite the experimental developments, computer simulations are needed to perform a true approximation to understand the complex interactions that govern this system. Several methods have been explored to model this quantum phenomenon, mainly based on the quantum open systems theory. The evolution of approaches to the problem has gone from traditional methods which wouldn't consider the memory effects of the surroundings to more robust non-Markovian methods for the modelling of the system evolution with a better representation of environmental interactions. While quantum walks have proven to provide a mathematical framework for the study of energy transfer efficiency in the FMO complex, further characterization of operating conditions may lead to effective control and optimization of the system. We perform a parametric analysis about some physical features in the quantum regime involved during the quantum excitation process to get a comprehension about its non-trivial dependence on operation parameters. Thus, the analysis is conducted in terms of some relevant physical parameters in the system to track the complex global behavior in aspects as coherence, entanglement, decoherence times, transference times, and efficiency of the main process of energy capturing. As a complementary analysis from the derived outcomes, we compare those features for two different species as a suggestive possible roadmap to track genetic differences in the photosynthetic performance of the complex through its biological nature.

Quantum phenomena on life systems: a parametric deep view on the Fenna-Mathews-Olson complex

A variable behaving as a quantum in economic system is studied on the basis of quantum mechanics. The several formulas of relevant variable are derived along with this speculation. Thus a possible value for the common constant which may be understood as Planck constant in economic system is calculated. There, a concerned variable seems to exhibit a quantum behavior.
Recently it has been pointed out that there might be a similarity between the rational expectation hypothesis in economics and quantum mechanics, where their observers are both in respective systems. Nevertheless, on the other hand, the principle of uncertainty in economics has not yet been discovered so far. Therefore we will study on this problem by starting to formulate the basic equations respective which correspond to quantum mechanics. Here we pursue solely a behavior of certain representative variable with which an important econophysical quantity is newly introduced, and then discuss about Planck constant in economic system.


A variable behaving as a quantum in economic system

Relative quantum complexity is the measure of state distance between two quantum states. In quantum circuits, it could be argued as the number of fundamental quantum logic gates required to change the initial state of a quantum system to another state. From the Penrose diagrams of Ads/CFT black holes, it has been analyzed that the volume of black holes increases with time. The astounding similarity between the growth of quantum complexity and the volume of black holes is believed to be the fundamental postulate to quantize gravity. Here, we implement a simulation model to demonstrate the power of one clean qubit. We explicate how addition of one clean qubit could increase the uncomplexity of a maximally complex state. We explore the clean qubit computation in IBM quantum experience platform by designing the circuits and running them on IBM QASM simulator. This one clean qubit computation is realized for maximally complex five states made of single-, two-, three-, four-, and five-qubit systems and the results are discussed by comparing the power of one thermal photon on the accessible spacetime of an observer near the black hole horizon.

Simulation Model for complexity in Blackholes and demonstration of power of clean qubit using IBM QX

At present, the surface-electrode ion trap is an important device to realize large-scale and integrated quantum information processing. However, there are still a series of problems in the fabrication process of the surface-electrode ion trap, the biggest disadvantage is that the surface topography is difficult to control during the fabrication. The rougher the surface, the worse the electrical and trapping ability of the surface-electrode ion trap. Therefore, we propose a micro-nano technology to control topography of surface-electrode ion trap, which is suitable for the fabrication of most surface electrode ion traps. In addition, based on the proposed micro-nano technology of controlling surface topography, we give a method to fabricate surface electrode ion trap with specific surface roughness, and successfully fabricated surface electrode ion traps with roughness of 6.2 nm to 45 nm. Experiments have proved that the technology of controlling surface roughness is feasible and repeatable. By fabricating surface-electrode ion traps with different topogrphy, we may have a deeper understanding of the influence of surface roughness on the trap performance, especially in electrical performance, heating rate, ion trapping ability and other aspects.

Micro-nano technology for controlling the surface topography of thick film surface-electrode ion trap

A silicon wafer based platform consisting of quantum nano pillars is presented in terms of quantum sensing and imaging. The pillars can be fabricated on silicon wafers using plasma processing under chlorine atmosphere. The pillars so produced on silicon wafers are still crystalline and their surfaces can be smoothed under control. The density of the pillars is very high, that is ⁓1010 cm-2. They have a tapered like structure with tip ends of few atomic sizes, where quantum size effects are dominating optical properties, such as ultrafast radiative recombination down to femtosecond regime at blue spectral region, offering interesting applications of quantum information processing involving ultrafast optical switching. 
Quantum pillars form an interesting application platform for identifying of chemical and biological species. The ensemble of quantum pillars can accommodate related species for subsequent measurements using quantum qubit systems such as diamond NV centers. 


Silicon quantum pillars for quantum sensing and imaging

We estimate the influence of passive source side channels on the BB84 decoy-state protocol. We use additional degrees of freedom as a model of side channels to calculate secret key rates for the intercept-resend attack, the unitary individual attack, and the unitary collective attack. We use a connection between this model and the Hong-Ou-Mandel (HOM) visibility to show that for state-of-the-art sources, used in quantum key distribution (QKD), the presence of passive source side channels does not reduce the security of the protocol significantly.

Upper-bounding source side-channel attack on the BB84 decoy-state protocol

From academia to industry, the field of quantum technologies is highly collaborative as we enter the second quantum revolution. 
QURECA (Quantum Resources and Careers) aims to create a link between the different stakeholders in the quantum community through a common language, and to generate global opportunities with quantum technologies. QURECA provides a range of professional services, and the solution to the quantum workforce skills bottleneck: the first online platform for quantum training and resourcing.
One of the main reasons QURECA was created was to tackle the “quantum bottleneck” that our society is experiencing. A reason for this being that many PhD students and graduates in the field struggle to apply their skillset and understand how it can assist in their career development.
Whether you are looking for your ideal job, to enhance your skillset or to find out more about opportunities in quantum, discover how your expertise can be useful and how to start your quantum career path!

Careers in quantum technologies

A nonlinear phase shift is introduced to a Mach‐Zehnder interferometer (MZI), and we present a scheme for enhancing the phase sensitivity. In our scheme, one input port of a standard MZI is injected with a coherent state and the other input port is injected with one mode of a two‐mode squeezed‐vacuum state. The final interference output of the MZI is detected with the method of active correlation output readout. Based on the optimal splitting ratio of beam splitters, the phase sensitivity can beat the standard quantum limit and approach the quantum Cramér‐Rao bound (QCRB). The effects of photon loss on phase sensitivity are discussed. Our scheme can also provide some estimates for units of χ(3), due to the relation between the nonlinear phase shift and the susceptibility χ(3) of the Kerr medium.

Nonlinear phase estimation enhanced by an actively correlated Mach‐Zehnder interferometer

The problem of dynamical charge carriers in a nanowire double quantum dots system under the influence of Dresshaul, Rashba spin-orbit coupling and Zeeman energy is introduced for comprehensive quantum theory and semiquantum approximation. The energy eigenvalues via shifted 1/N expansion is calculated as a function of the roots corresponding to quantum states and the semiconductor nanowire double quantum dots parameters. We find out that the Coulomb energy decreases while the magneto-confining energy increases whilst the quantum state changes. The gallium arsenide nanowire double quantum dots is in good agreement with representation of the true ground state at all values of the resulting Dresselhaus and Rashba spin-orbit coupling parameters.

The understanding of spin-orbit effects in a nanowire double quantum dots system

Encoding discrete variables into qubits is an important task for applying quantum computing to combinatorial optimisation problems, both under the context of quantum annealing and gate model algorithms such as QAOA. Traditionally discrete variables are encoded by implementing a 'one hot' constraint on a set of qubits. I demonstrate that a superior method to encode such variables is to encode them as a domain wall on an Ising chain as discussed in [1]. I discuss how this method works and present numerical evidence for it's superior performance. As an extreme example, in some cases for quantum annealing using a domain wall encoding instead of one hot can have as much impact as completely re-engineering the hardware. I also discuss the cases in which unary encodings (one hot or domain wall) may be preferable to binary encodings or vice-versa. I further discuss how this encoding can be used in quantum simulation of field theories as discussed in [2]

[1] Chancellor N 2019 Quantum Sci. Technol. 4 045004 https://doi.org/10.1088/2058-9565/ab33c2

[2] Abel S, Chancellor N, Spannowsky M https://arxiv.org/abs/2003.07374 (see also: arXiv:2006.06003)

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