High-Rate Quantum Communications
Lead Research Organisation:
University of York
Department Name: Computer Science
Abstract
Quantum information is gradually moving towards practical implementations. This is the new field of quantum technologies, a broad area where quantum communications and, in particular, quantum cryptography are progressing the most. Prototypes of secure quantum networks are currently being built and the basic elements of a future
quantum Internet are being advanced at a promising pace.
This PhD studentship is aimed at exploring the ultimate limits of quantum cryptography with or without the use of repeaters, which may be trusted or untrusted. Research will be focused on determining the secret key capacity of some of the most relevant quantum channels as well as designing practical high-rate protocols that are able to
approximate such ultimate performances. Background in quantum information and/or quantum optics is advised. The work will also involve the simulation and analysis of a high-rate secure quantum networks.
One of the investigations will be focused on the study of "butterfly" networks, in order to show how their topology is particularly deleterious for transmitting quantum information. This study allows us to fully understand which architectures should be avoided in the construction of quantum networks. The analysis will be first carried out using discrete-variable systems (qubits) and then extended to continuous-variable systems, such as the bosonic modes of the optical field. This analysis will then be extended to identifying favourable network topologies, especially with the aim of establishing secret keys between two end-nodes.
Finally, we will attempt to generalize techniques of measurement-device independence to a network scenario, so that we can realize a high-rate secure quantum network which is based on the end-to-end principle. This would be an important step towards the construction of a realistic quantum network which is robust with respect to the presence of unreliable and untrusted middle nodes.
quantum Internet are being advanced at a promising pace.
This PhD studentship is aimed at exploring the ultimate limits of quantum cryptography with or without the use of repeaters, which may be trusted or untrusted. Research will be focused on determining the secret key capacity of some of the most relevant quantum channels as well as designing practical high-rate protocols that are able to
approximate such ultimate performances. Background in quantum information and/or quantum optics is advised. The work will also involve the simulation and analysis of a high-rate secure quantum networks.
One of the investigations will be focused on the study of "butterfly" networks, in order to show how their topology is particularly deleterious for transmitting quantum information. This study allows us to fully understand which architectures should be avoided in the construction of quantum networks. The analysis will be first carried out using discrete-variable systems (qubits) and then extended to continuous-variable systems, such as the bosonic modes of the optical field. This analysis will then be extended to identifying favourable network topologies, especially with the aim of establishing secret keys between two end-nodes.
Finally, we will attempt to generalize techniques of measurement-device independence to a network scenario, so that we can realize a high-rate secure quantum network which is based on the end-to-end principle. This would be an important step towards the construction of a realistic quantum network which is robust with respect to the presence of unreliable and untrusted middle nodes.
People |
ORCID iD |
| Stefano Pirandola (Primary Supervisor) | |
| Kieran Wilkinson (Student) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509802/1 | 01/10/2016 | 31/03/2022 | |||
| 1949872 | Studentship | EP/N509802/1 | 01/08/2017 | 31/07/2020 | Kieran Wilkinson |
| Description | With the highly desirable promise of unbreakable security against any attack allowed by the laws of physics, quantum cryptography is of interest not just in an academic setting but to many sectors across the market. Unfortunately, many of the existing cryptographic protocols are difficult to implement without expensive equipment. Continuous-variable quantum cryptography offers an alternative regime that can be implemented with readily available and inexpensive hardware while achieving very high communication rates close to the fundamental limit. The caveat is that many existing protocols are confined to short distances. This project has enabled the development of protocols that significantly increase the range of continuous-variable protocols, helping to bridge the distance gap between continuous-variable protocols and the more difficult to implement discrete-variable protocols. The research has considered point-to-point protocols with thermal states, allowing lower-frequency radiation to be used rather than being confined to visible optics. It has also considered measurement-device-independent (MDI) protocols in which parties communicate via an untrusted relay. MDI protocols are desirable as they remove the threat of side-channel attacks possible in point-to-point alternatives. Continuous-variable MDI protocols have been demonstrated to achieve particularly high secret key rates; however, communication is limited to very short distances if the relay is positioned equidistant between the parties. The protocol developed as part of this project increases the maximum distance achievable in continuous-variable MDI cryptography and work has started on a proof-of-principle experiment at a collaborating university. The production of these protocols has led to the development of a software package that can assist with further investigations in continuous-variable quantum cryptography, reducing the burden of the computational work required. One of the other goals of this project was to examine the butterfly-network structure in a quantum network. It is known that with classical communications it is possible to effectively communicate two bits through a butterfly network bottleneck channel using a technique known as network coding. Our research shows mathematically that this is not possible in the quantum regime. We have extended our analysis to larger networks built with butterfly blocks and found that the gap between the communication rate of the classical and quantum regimes increases as more butterfly networks are added in parallel. These results provide an early warning that butterfly network structures should be avoided when constructing quantum network infrastructure. It also means that we cannot implement quantum networking into existing networks containing butterfly structures without a reduction in the communication rate. These results open up a question about an alternative to butterfly network structures that allow efficient quantum communications in future infrastructure. |
| Exploitation Route | Our results have shown that butterfly network structures are detrimental to quantum communications, but further work may enable the development of new network structures that enable allow high-rate quantum communications with minimum resources. The quantum cryptographic protocols designed as part of this project provide a building block for further protocols in continuous-variable quantum cryptography which may be applied by researchers to other network structures or may be modified in such a way as to further increase the range of point-to-point or single-relay-assisted communications. Furthermore, a proof-of-principle experiment of one of our protocols is already in development at a collaborating university and as continuous-variable quantum cryptography is easily implementable with existing technology, an in-field test of one or more of our protocols could be possible in the near future by an experimentalist team at a university of a private company with a desire for highly secure communications. |
| Sectors | Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software) |
| Description | Proof-of-principle experiment collaboration |
| Organisation | Technical University of Denmark |
| Country | Denmark |
| Sector | Academic/University |
| PI Contribution | We have developed a long-distance continuous-variable quantum-key-distribution protocol |
| Collaborator Contribution | DTU are designing a proof-of-principle experiment for the protocol. |
| Impact | The experiment is still under development. |
| Start Year | 2020 |
| Title | Continuous-variable quantum-key-distribution module |
| Description | The software is a FORTRAN module that contains several functions that are used in the analysis of continuous-variable quantum mechanics, particularly quantum cryptography. |
| Type Of Technology | Software |
| Year Produced | 2020 |
| Impact | The package significantly speeds up the development of new cryptographic protocols as the functions from the module can be reused. |