Wed 19th Feb
Thur 20th Feb
TITLES and ABSTRACTS
Clement Meignant, LIP6
Title: Communicating over quantum networks using network coding
Hayata Yamasaki , U. Tokyo
Title: Resources required for encoding/decoding quantum information over networks
William John Munro, NTT Basic Research Lab
Title: Designing large scale quantum networks and routing information around them
Abstract: It is now well known that quantum physics offers novel ways for information communication. It is expected that these principles will lead to a quantum enabled internet supporting new communication, computation, sensing and imaging tasks. Given the global nature of such an internet, it is clear that quantum repeaters will play an essential role in both its development and abilities. Many of the essential elements required for such networks have already demonstrated in the laboratory. We are at the stage where many of these elements are being integrated together, however the communities focus has been on small scale networks whose topology makes the of routing of quantum signals quite forward. Moving forward we need to explore how routing will work on this larger scale quantum networks especially when the networks entire topology is not known to all users of that network. We will discuss various routing options that are available and show these impose quite different constraints on the fundamental building blocks of the network. This will be illustrated with a number of examples including several with no classical analog.
Josephine Dias, NII
Title: Quantum repeaters for continuous variables
Abstract: The need for long distance distribution of quantum states is crucial for many applications of quantum technology including quantum key distribution, teleportation of quantum states, and quantum networks. However, quantum optical states are fragile and can become corrupted when passed through a lossy communication channel. Quantum repeaters have been proposed as a way of increasing the range of quantum communications. Current protocols target specific discrete encodings, for example quantum bits encoded on the polarization of single photons. We introduce a general approach that can reduce the effect of loss on any quantum optical encoding, including those based on continuous variables such as field amplitudes.
Robert Booth, LIP6
Title: Flow Conditions for Continuous Variable Measurement-based Quantum Computing
Abstract: We introduce flow-based methods for continuous variables graph states, inspired by the notions of flow and g-flow for discrete variables measurement-based quantum computing. This allows us to formulate a protocol for measurement-based quantum computing in continuous variables using arbitrary entanglement topologies. Furthermore, we give a necessary and sufficient condition for our protocol to converge in the limit of infinite squeezing and perfect measurements. Like for discrete variables, these constructions are useful for determining when an arbitrary CV graph state can be used for a practical computation. These results also extend the discrete variables methods to MBQC with qudits of any local dimension.
Ulysse Chabaud, LIP6
Title: Stellar representation of non-Gaussian states
Abstract: Non-Gaussian states are needed for achieving universal quantum computing with continuous variables, and are crucial for many other applications in continuous variable quantum information processing such as state distillation or error-correction. The stellar formalism allows to represent non-Gaussian properties of single-mode quantum states by the distribution of the zeros of their Husimi Q function in phase space. We use this representation in order to unveil the structure of single-mode continuous variable quantum states: we derive an infinite hierarchy of single-mode states based on the number of zeros of the Husimi Q function, the stellar hierarchy. We give an operational characterisation of the states in this hierarchy and derive equivalence classes under Gaussian unitary operations. We study in detail the topological properties of this hierarchy with respect to the trace norm, and discuss implications for non-Gaussian state engineering, and continuous variable quantum computing.
Nicolo Lo Piparo, NII
Title: Resource reduction for distributed quantum information processing using quantum multiplexed photons
Abstract: Distributed quantum information processing is based on the transmission of quantum data over lossy channels between quantum processing nodes. These nodes may be separated by a few microns or on planetary scale distances, but transmission losses due to absorption/scattering in the channel are the major source of error for most distributed quantum information tasks. Of course quantum error detection (QED) /correction (QEC) techniques can be used to mitigate such effects but error detection approaches have severe performance issues due to the signaling constraints between nodes and so error correction approaches are preferable - assuming one has sufficient high quality local operations. Typical loss based QEC utilizes a one qubit per photon encoding. However single photons can carry more than one qubit of information and so our focus in this work is to explore whether loss-based quantum error correction utilizing quantum multiplexed photons is viable and advantageous, especially as photon loss results in more than one qubit of information being lost.
Nathan Shettell, LIP6 / NII
Title: Quantum metrology using graph states
Abstract: The field of quantum metrology has been on the rise for the past few years, and has many near term applications in a variety of scientific domains. In essence, quantum metrology uses quantum probes to measure physical quantities, and entanglement between probes allows us to achieve a precision superior to the classical analogue. However, entanglement is not a sufficient condition to gain a quantum advantage. As such, it is an interesting question to determine which quantum states are advantageous for quantum metrology. This talk is divided into two sections. The former being an introduction to quantum metrology, in which the relevant statistics and nomenclature are reviewed. While the latter explores the practicality of graph states for quantum metrology and we construct a class of graph states (named bundled graph states) which approximately achieves the Heisenberg limit.
Marta P Esterellas, NII
Title: Efficient compression of braided circuits
Abstract: Mapping an arbitrary quantum algorithm to any practical large-scale quantum computer needs a set of compilations and optimizations. At the level of fault-tolerant encoding, one likely requirement of this process is the translation into a topological circuit, being braided circuits one of the candidate models. Given the added overhead of such circuits, it is paramount to reduce their resources (e.g. computation time and number of physical qubits required) through compression of the braided circuit. We note that while these optimizations have typically been performed in the language of 3-dimensional diagrams, such representation does not allow for an efficient, general and scalable optimization nor its verification. We propose the use of the ZX-calculus as an intermediate representation for the compression of general topological braided based circuits. We show the advantages of this representation by comparing the results using the ZX-Calculus with those previously obtained in the 3D representation for the compression of the distillation circuits of the |Y⟩ and |A⟩ magic states. The benchmarking of our method against a set of arbitrary circuits yields compression percentages of ~80% the original volume, backing up the importance of the ZX-Calculus in the resource optimization of topological braided circuits.
Koji Azuma, NTT Basic Research Lab
Title: Bounding capacities of quantum internet protocols
Abstract: Bounding quantum and private capacities of quantum internet protocols is a fundamental building block to design the routing in the future quantum internet. In this talk, we present an efficient linear program to bound capacities of quantum internet protocols, as well as upper/lower bounds. This program is applied to bipartite cases, multi-pair cases, and a multi-partite case.
Marco Tulio Quintino
Title: Implementation of inverse of an unknown unitary
Title: Quantum position verification