Ronald J. Sadlier

Software-defined quantum communication systems

Abstract. Quantum communication (QC) systems harness modern physics through state-of-the-art optical engineering to provide revolutionary capabilities. An important concern for QC engineering is designing and prototyping these systems to evaluate the proposed capabilities. We apply the paradigm of software-defined communication for engineering QC systems to facilitate rapid prototyping and prototype comparisons. We detail how to decompose QC terminals into functional layers defining hardware, software, and middleware concerns, and we describe how each layer behaves. Using the superdense coding protocol as an example, we describe implementations of both the transmitter and receiver, and we present results from numerical simulations of the behavior. We conclude that the software-defined QC provides a robust framework in which to explore the large design space offered by this new regime of communication.

Programmable Multi-Node Quantum Network Design and Simulation

Software-defined networking offers a device-agnostic programmable framework to encode new network functions. Externally centralized control plane intelligence allows programmers to write network applications and to build functional network designs. OpenFlow is a key protocol widely adopted to build programmable networks because of its programmability, flexibility and ability to interconnect heterogeneous network devices. We simulate the functional topology of a multi-node quantum network that uses programmable network principles to manage quantum metadata for protocols such as teleportation, superdense coding, and quantum key distribution. We first show how the OpenFlow protocol can manage the quantum metadata needed to control the quantum channel. We then use numerical simulation to demonstrate robust programmability of a quantum switch via the OpenFlow network controller while executing an application of superdense coding. We describe the software framework implemented to carry out these simulations and we discuss near-term efforts to realize these applications.

Superdense Coding over Optical Fiber Links with Complete Bell-State Measurements

Adopting quantum communication to modern networking requires transmitting quantum information through a fiber-based infrastructure. We report the first demonstration of superdense coding over optical fiber links, taking advantage of a complete Bell-state measurement enabled by time-polarization hyperentanglement, linear optics, and common single-photon detectors. We demonstrate the highest single-qubit channel capacity to date utilizing linear optics, 1.665±0.018, and we provide a full experimental implementation of a hybrid, quantum-classical communication protocol for image transfer.

Superdense Coding Interleaved with Forward Error Correction

Abstract Superdense coding promises increased classical capacity and communication security but this advantage may be undermined by noise in the quantum channel. We present a numerical study of how forward error correction (FEC) applied to the encoded classical message can be used to mitigate against quantum channel noise. By studying the bit error rate under different FEC codes, we identify the unique role that burst errors play in superdense coding, and we show how these can be mitigated against by interleaving the FEC codewords prior to transmission. We conclude that classical FEC with interleaving is a useful method to improve the performance in near-term demonstrations of superdense coding.

Software-defined Quantum Communication Systems

We show how to extend the paradigm of software-de ned communication to include quantum communication systems. We introduce the decomposition of a quantum communication terminal into layers separating the concerns of the hardware, software, and middleware. We provide detailed descriptions of how each component operates and we include results of an implementation of the super-dense coding protocol. We argue that the versatility of software-de ned quantum communication test beds can be useful for exploring new regimes in communication and rapidly prototyping new systems.

Bell state optimizations for reliable quantum applications

Well-defined and stable quantum networks are essential to realize functional quantum communication applications. In particular, the quantum states must be precisely controlled to produce meaningful results. To counteract the unstable phase shifts in photonic systems, we apply local Bell state measurements to calibrate a non-local quantum channel. The calibration procedure is tested by applying a time encoded quantum key distribution procedure using entangled photons.

Software-defined quantum network switching

We present the design and implementation of a software-defined quantum networking protocol and software switch integrated with a numerical quantum channel simulator. Our protocol design leverages recent advances in the OpenFlow protocol that enable software-defined control and management of optical network traffic using side-channel metadata. We implement this design using customization of the open source vSwitch for optical network routing, and we test the implementation using a numerical simulator of the quantum channel alongside actual network traffic. Our results support the integration of quantum communication with existing optical transport methods.

Demonstration of provably secure quantum key distribution (QKD)

Optimized Quantum Key Distribution (QKD) protocols revolutionize the cyber security by leveraging the quantum phenomenon for development of unbreakable security. Configurable quantum networks are necessary for accessible quantum applications amongst multiple users. Quantum key distribution is particularly interesting because of the many ways in which the key exchange can be carried out. Keys can be exchanged by encoding the key into a weak photon source using classical methods, or the keys can be exchanged using pairs of photons entangled at the source, or the keys can even be exchanged by encoding with classical hardware at the source with an entangling measurement which occurs at the photons destination. Each type of quantum key exchange has its own requirements that must be met for point-to-point implementations which makes it exceedingly difficult to implement multi-node quantum networks. We propose a programmable network model to time encoded quantum key distribution; this version of QKD sends entangled photons to two users and the hardware is setup such that the relative time shift in the coincident photons encodes which measurement basis was used. The protocols were first simulated by modifying previous software which used the CHP quantum simulator, and then a point-to-point key exchange was setup in hardware to demonstrate the time encoding aspects of the protocol.

Superdense coding for quantum networking environments

Quantum networks provide a versatile infrastructure for communication, computing, and sensing with quantum information. Novel sources and detectors for transmitting and receiving quantum states are critical elements in the development and eventual deployment of robust quantum networks. Alongside performance, the compatibility of quantum network devices with modern networking infrastructure is an important requirement for deployment. We present results on the integration of quantum communication using superdense coding transmitted over optical fiber links into network environments. Our approach takes advantage of a novel complete Bell-state measurement setup that relies on hyper-entanglement in the temporal and polarization degrees of freedom for a two-photon state emitted from a quantum light source. Using linear optics and common single-photon detectors, we record a single-qubit channel capacity of 1.665±0.018. We then demonstrate a full experimental implementation of hybrid, quantum-classical communication protocol for image transfer applications. Our devices integrate with existing fiber optical network and software-defined transmitters and receivers as part of a modular design to provide an extensible quantum communication system that can adapt to future quantum technology goals.

Software-defined network abstractions and configuration interfaces for building programmable quantum networks

Well-defined and stable quantum networks are essential to realize functional quantum communication applications. Quantum networks are complex and must use both quantum and classical channels to support quantum applications like QKD, teleportation, and superdense coding. In particular, the no-cloning theorem prevents the reliable copying of quantum signals such that the quantum and classical channels must be highly coordinated using robust and extensible methods. In this paper, we describe new network abstractions and interfaces for building programmable quantum networks. Our approach leverages new OpenFlow data structures and table type patterns to build programmable quantum networks and to support quantum applications.