Session S45: Status of Quantum Networks

Running applications on a quantum network

A quantum network enables applications that are impossible or inefficient using any form of classical networking. Here, we present an architecture for executing quantum applications on a network of quantum processors, and report on their implementation on a two-node quantum network testbed in the lab. We will also highlight several analytical tools and algorithms developed in this context, that may be of broad interest for the analysis and near-term implementation of quantum networks.   

Cyber Risk Mitigation in the Era of Quantum Computing

Cryptographically relevant quantum computers (CRQC) can break standard encryption schemes such as RSA and forge digital identity and digital signatures, thus creating chaos in our financial transactions and threatening the security of our critical infrastructure. Large IT corporations such as Google and IBM are racing to build CRQC, possibly by 2030. Indeed, the “harvest now and decrypt later” attack may threaten our communication security even today.

In this talk, I will review the quantum threat to cyber-security. Moreover, I will briefly review the three classes of methods to counter this quantum threat including quantum-resistant conventional cryptography (often called post-quantum cryptography (PQC)), quantum key distribution (QKD), and pre-shared keys (PSK). I argue that they form the three pillars needed to address this immense security challenge.

PQC is currently being standardized by NIST, but it can never be proven to be fundamentally secure. The immense progress in the key rate and security of QKD over the last few decades will be reviewed together with the unappreciated importance of PSK solutions for securing our long-term secrets.   

What can 10 qubits do to solve classification problems?

In the last few years, the size of quantum processors has increased roughly by an order of magnitude in terms of the number of qubits.  This rapid growth has encouraged significant efforts to find suitable applications for these noise quantum processors.  So far, however, the accumulated evidence shows its difficulties, and it seems that it is not so easy to extract the practical computational power out of these devices, which are otherwise capable to create complex dynamics.  In this talk, we present a new approach to use such complex quantum dynamics for a practical computational task.  As a concrete example, we show a computational model based on quantum neural networks referred as quantum extreme reservoir computation (QERC).  The performance of this model is evaluated by solving classification problems and a comparison to the classical approach with a similar resource. 

This model was initially designed using the network structure virtually imbedded on the Hilbert space.  To investigate the relation of the computational power as the QERC and the network property of the unitary map on the Hilbert space, we analyze the unitary map created by the quantum reservoir dynamics and show a certain property can help the performance on solving these classification problems.   

Entanglement of Nanophotonic Quantum Memory Nodes in a Telecommunication Network

A key challenge in realizing practical quantum networks for long-distance quantum communication involves robust entanglement between quantum memory nodes connected via fiber optical infrastructure. Here, we demonstrate a two-node quantum network composed of multi-qubit registers based on silicon-vacancy (SiV) centers in nanophotonic diamond cavities integrated with a telecommunication fiber network. Remote entanglement is generated via the cavity-enhanced interactions between the SiV's electron spin qubits and optical photons. Serial, heralded spin-photon entangling gate operations with time-bin qubits are used for robust entanglement of separated nodes. Long-lived nuclear spin qubits are used to provide second-long entanglement storage and integrated error detection. By integrating efficient bi-directional quantum frequency conversion of photonic communication qubits to telecommunication frequencies (1350 nm), we demonstrate entanglement of two nuclear spin memories through 40 km spools of low-loss fiber and a 35 km long fiber loop deployed in the Boston area urban environment, representing an enabling step towards practical quantum repeaters and large-scale quantum networks.   

Quantum networking with trapped ions in optical cavities

Envisioned quantum networks [1] would open up powerful new applications in information security, distributed computing, precision sensing, and timekeeping. These applications require distributed quantum network nodes that, first, can be entangled via the exchange of photons over long distances and, second, can store and process quantum information encoded in registers of qubits.

 

In this talk I will present our realization of a quantum network node based on a register of trapped calcium ions interfaced with photons via a high finesse optical cavity. The node combines capabilities of high-efficient single-photon emitter with local deterministic quantum logic and information storage. I will then present results of proof of principle experiments, enabled by those capabilities. These experiments include demonstrations of: (i) entanglement between two nodes placed in different buildings [2], (ii) quantum repeater node operating over a 50km long fiber channel [3],  and (iii) multiplexed ion-photon entanglement and its distribution over 101 km of optical fiber (4). The talk will be concluded with the most recent results, prospects and limitations of our platform.

 

[1] H. J. Kimble, The quantum internet, Nature (London) 453 (2008)

[2] V. Krutyanskiy, M. Galli, et el., Entanglement of Trapped-Ion Qubits Separated by 230 Meters, Phys. Rev. Lett. 130  (2023).

[3] V Krutyanskiy, M Canteri, M Meraner, J Bate, V Krcmarsky, J Schupp, N. Sangouard, B. Lanyon, Telecom-wavelength quantum repeater node based on a trapped-ion processor Phys. Rev. Lett. 130  (2023)

[4]  V Krutyanskiy, M Canteri, M Meraner, V Krcmarsky, BP Lanyon, Multimode ion-photon entanglement over 101 kilometers of optical fiber, arXiv preprint arXiv:2308.08891 (2023)