Final Report Summary - QORE (Quantum Correlations)
QORE is built around a multifaceted approach encompassing Theory, Experiments & Applications. The QORE project has been incredible fruitful in better understanding quantum correlations and putting them to use through both pure and applied, as well fundamental and application oriented experiments that take advantage of, or test, aspects of quantum correlations. The project produced over 40 publications, numerous associated news stories and the work has been presented at numerous conferences in its five years. In the following we will simply highlight a few key results.
Tests of non-locality have a long history that arose out of the famous Bell inequalities. Historically, this has mostly focused on relatively simple two-party scenarios. While we have continued to work on many outstanding problems in this regime we have made extensive progress on multi-party scenarios. In particular, we found an inequality to study the question of whether non-locality based on finite-speed causal influences leads to superluminal signalling [1]. This deep and fascinating result opens the door to both theoretical and experimental studies at the interface of quantum and relativistic physics illustrating the difficulty to modify quantum physics while maintaining no-signalling. Building on these multi-party concepts we made significant contribution in terms of simulating complexity [2] and bi-locality [3], e.g. for entanglement swapping experiments. We also proposed [4] and recently collaborated on experimentally [5] demonstrating genuine multipartite entanglement with a device-independent witness. The concept of Device Independent” is fundamentally related to non-locality. In this context we proposed the first scheme for device-independent quantum key distribution [6], which exploited the novel concept of heralded photon amplification. This amplification has subsequently been experimentally demonstrated by several groups including ours.
A significant experimental effort was dedicated to developing advanced quantum memories with a view to increasing the distance over which quantum systems can be distributed, i.e. via quantum repeaters. We were able to demonstrate the first telecom wavelength quantum memory [7], however, various limitations associated with the materials forced us to change from Er-doped solid-state quantum memories to Nd-doping. This has been much more productive and progress has been excellent. We demonstrated how we could entangle these quantum memories with telecommunication wavelength photons via entangled photon pair sources [8]. We went on to further adapt these promising systems for the storage of polarisation encoded qubits.
A more applied effort looked at real world applications of quantum key distribution (QKD), based on quantum correlations. This again bridged theory and experiment. An important aspect of the theory effort was highlighted by our work on the security analysis of these systems when one considers limited key lengths – so-called finite keys [9]. We also devised a novel and practical quantum protocol based on QKD, for private database queries [10]. The rest of the effort worked towards high-speed and long-distance QKD. We were able to demonstrate QKD over 250kms of fibre [11], which until just recently was the world record (now standing at 260kms). In a more advanced system, and over shorter distances, we have made several experiments including running QKD along with 1 Gbps data encryption over a single fibre. This latter experiment marking an important practical landmark in dealing with standard classical links integrated via standard telecom DWDM technology [12].
Tests of non-locality have a long history that arose out of the famous Bell inequalities. Historically, this has mostly focused on relatively simple two-party scenarios. While we have continued to work on many outstanding problems in this regime we have made extensive progress on multi-party scenarios. In particular, we found an inequality to study the question of whether non-locality based on finite-speed causal influences leads to superluminal signalling [1]. This deep and fascinating result opens the door to both theoretical and experimental studies at the interface of quantum and relativistic physics illustrating the difficulty to modify quantum physics while maintaining no-signalling. Building on these multi-party concepts we made significant contribution in terms of simulating complexity [2] and bi-locality [3], e.g. for entanglement swapping experiments. We also proposed [4] and recently collaborated on experimentally [5] demonstrating genuine multipartite entanglement with a device-independent witness. The concept of Device Independent” is fundamentally related to non-locality. In this context we proposed the first scheme for device-independent quantum key distribution [6], which exploited the novel concept of heralded photon amplification. This amplification has subsequently been experimentally demonstrated by several groups including ours.
A significant experimental effort was dedicated to developing advanced quantum memories with a view to increasing the distance over which quantum systems can be distributed, i.e. via quantum repeaters. We were able to demonstrate the first telecom wavelength quantum memory [7], however, various limitations associated with the materials forced us to change from Er-doped solid-state quantum memories to Nd-doping. This has been much more productive and progress has been excellent. We demonstrated how we could entangle these quantum memories with telecommunication wavelength photons via entangled photon pair sources [8]. We went on to further adapt these promising systems for the storage of polarisation encoded qubits.
A more applied effort looked at real world applications of quantum key distribution (QKD), based on quantum correlations. This again bridged theory and experiment. An important aspect of the theory effort was highlighted by our work on the security analysis of these systems when one considers limited key lengths – so-called finite keys [9]. We also devised a novel and practical quantum protocol based on QKD, for private database queries [10]. The rest of the effort worked towards high-speed and long-distance QKD. We were able to demonstrate QKD over 250kms of fibre [11], which until just recently was the world record (now standing at 260kms). In a more advanced system, and over shorter distances, we have made several experiments including running QKD along with 1 Gbps data encryption over a single fibre. This latter experiment marking an important practical landmark in dealing with standard classical links integrated via standard telecom DWDM technology [12].