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Jul 10, 2023

Research Roundup for August 2024

By Dr Chris Mansell, Senior Scientific Writer at Terra Quantum Shown below are summaries of a few interesting research papers in quantum technology that we have seen over the past month. Title:

By Dr Chris Mansell, Senior Scientific Writer at Terra Quantum

Shown below are summaries of a few interesting research papers in quantum technology that we have seen over the past month.

Title: High-efficiency single photon emission from a silicon T-center in a nanobeamOrganizations: University of Maryland; Simon Fraser University; Photonic Inc.Optically active solid-state qubits are important for quantum computers, networks, and sensors. Integrating these qubits with nanophotonic devices enhances photon emission and light-matter interactions. The researchers employed a nanobeam structure that efficiently emitted light in a mode matched to a lensed single-mode fiber, allowing them to collect more than 70% of the T center’s emission. This is the highest T center count rate so far documented. The next stride forward will involve coupling the zero phonon line to a cavity mode to enhance the brightness.Link: https://arxiv.org/abs/2308.04541

Title: Scalable Multipartite Entanglement Created by Spin Exchange in an Optical LatticeOrganizations: University of Science and Technology of China; Fudan University; Tsinghua UniversityOptical superlattices are the natural system for performing parallel operations on ultracold atoms while quantum gas microscopes excel at single-atom manipulation. Here, these technologies were combined with digital micromirror devices to create and detect large-scale multipartite entanglement. This architecture allowed layers of quantum gates to be applied to atoms separated at moderate distances. The researchers successfully prepared Bell states with both a high fidelity and a long lifetime, and then extended this entanglement to more complex states involving one-dimensional chains and two-dimensional plaquettes. They verified this entanglement using rigorous criteria.Link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.073401

Title: The debate over QKD: A rebuttal to the NSA’s objectionsOrganization: ETH ZurichThe NSA is sceptical about quantum key distribution (QKD). Their perspective is that QKD is a costly, yet partial, solution that is challenging to implement, requires special purpose equipment and increases the risks of insider threats and denial of service attacks. They conclude that these limitations currently make it unsuitable for use. A new preprint has offered counterarguments to each of the NSA’s points. The authors contest some of the claims, deeming them unjustified, while acknowledging that other issues exist but could likely be resolved in the foreseeable future. They list the technical constraints highlighted by the NSA and explain their stance on each, considering their validity in the short, medium, and long term.Link: https://arxiv.org/abs/2307.15116

Title: Potential Energy Advantage of Quantum EconomyOrganizations: The University of Chicago; qBraid Co.; SeQure Co.; University of Toronto; University of Hong KongThis study focuses on the escalating energy demands of the modern computing sector due to the widespread use of large-scale machine learning and language models. It addresses the significance of energy conservation for computing service providers in terms of their market expansion and compliance with governmental regulations. The authors assess the possibility of quantum computing having an energy advantage over classical computing. They suggest that quantum computing might offer a more sustainable trajectory for the computing industry but only when quantum computing is deployed at sufficient scale. Using real-world physical parameters, they quantify the operational scale required to achieve this energy-efficient edge.Link: https://arxiv.org/abs/2308.08025

Title: Modular Superconducting Qubit Architecture with a Multi-chip Tunable CouplerOrganization: Rigetti ComputingThe paper describes three different designs of multi-chip tunable couplers using vacuum gap capacitors or superconducting indium bump bonds to create a floating tunable coupler which mediate interactions between qubits on separate chips to build a modular architecture. The paper also shows that two-qubit gate operations between chips can have a fidelity at the same level as qubits with a tunable coupler on a single chip. Such a technology could be important for creating a modular and scalable quantum computer.Link: https://arxiv.org/abs/2308.09240

Title: Constant-Overhead Fault-Tolerant Quantum Computation with Reconfigurable Atom ArraysOrganizations: The University of Chicago; Harvard University; California Institute of Technology; University of Arizona; QuEra Computing Inc.This preprint proposes a practical method for fault-tolerant quantum computation using quantum low-density parity-check (qLDPC) codes on reconfigurable atom arrays. These codes offer high encoding rates but have experimentally challenging long-range connectivity requirements. The team devised an efficient approach that capitalizes on the product structure of qLDPC codes by using atom rearrangement to enable non-local syndrome extraction. They verified the fault tolerance of their protocols, conducted simulations of memory and logical operations, and found that their qLDPC-based setup outperforms the surface code in terms of qubit requirements. This opens the door to practical, low-overhead quantum computing using qLDPC codes and existing experimental techniques.Link: https://arxiv.org/abs/2308.08648

Title: High-threshold and low-overhead fault-tolerant quantum memoryOrganization: IBMThe researchers have developed a quantum error correction protocol consisting of an LDPC quantum code, a syndrome measurement circuit, and a decoding algorithm. The LDPC code has a high encoding rate and shows excellent performance in the near-threshold regime. Their protocol achieves an impressive error threshold of 0.8%, meaning that if the physical error rate of the quantum system remains below this value, practical error correction becomes feasible. This threshold is comparable to the well-established surface code’s performance. They demonstrated that their method preserves 12 logical qubits for ten million cycles using only 288 physical qubits, a substantial improvement over existing methods that would require over 4000 qubits. The hardware requirements to implement their scheme are relatively mild and could possibly be met by improved superconducting architectures.Link: https://arxiv.org/abs/2308.07915

Title: Schrödinger-Heisenberg Variational Quantum AlgorithmsOrganizations: University of Science and Technology of China; Shanghai Research Center for Quantum Sciences; Peking UniversityTo overcome the issue of NISQ devices having limited circuit depths, the authors of this paper introduce a new approach called Schrödinger-Heisenberg Variational Quantum Algorithms (SHVQAs). This method involves performing a noiseless classical simulation of a deep quantum circuit and running a shallow quantum circuit on a quantum processor. This is referred to as combining a virtual Heisenberg circuit with a real shallow Schrödinger circuit. Compared to the usual approaches to variational quantum algorithms, a much larger Hilbert space can be explored. Numerical experiments confirmed that SHVQAs were successful in approximating random states, improving solutions to quantum models, and simulating molecular structures. This work, along with effective error mitigation, advances accurate quantum algorithms on near-term quantum hardware.Link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.060406

Title: Autonomous quantum error correction and fault-tolerant quantum computation with squeezed cat qubitsOrganizations: The University of Chicago; University of Innsbruck; Institute for Quantum Optics and Quantum Information of the Austrian Academy of SciencesIn this paper, a quantum error correction scheme employing squeezed cat (SC) states was designed to combat excitation loss in continuous-variable quantum systems. By engineering the system’s environment or reservoir, the authors demonstrated that controlled dissipation can stabilize a two-component SC code while autonomously correcting the errors. The dissipation involves specific interactions between bosonic modes or between a bosonic mode and a qutrit. This scheme is applicable across various quantum platforms, like superconducting circuits and trapped-ion systems, and is a significant improvement on prior methods.Link: https://www.nature.com/articles/s41534-023-00746-0

Title: Experimental Benchmarking of an Automated Deterministic Error-Suppression Workflow for Quantum AlgorithmsOrganization: Q-CTRLThis article presents an autonomous workflow named “Fire Opal” that deterministically minimizes the errors that occur during a quantum computation, starting from gate-level operations to circuit execution and measurement. The workflow incorporates error-aware compilation, automatic system-wide gate optimization, dynamic decoupling, and efficient measurement-error mitigation. Extensive benchmarks were conducted on IBM hardware, showcasing over a thousand-fold enhancement compared to existing error-reduction techniques. The experiments covered various quantum algorithms and demonstrated the effectiveness of the approach by outperforming other methods. The findings highlight the role of Non-Markovian errors in algorithm performance and underscore the efficacy of the proposed deterministic error-suppression workflow.Link: https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.20.024034

Title: A Conceptual Architecture for a Quantum-HPC MiddlewareOrganizations: Utrecht University; Rutgers University; Brookhaven National Lab; Ludwig Maximilian University Munich; BMW GroupThe researchers considered the shift from single, monolithic quantum computing systems to more modular setups consisting of multiple quantum processing units interconnected with classical computing nodes. As the scale of these systems grows, so-called middleware systems become crucial to bridge the gap between quantum and classical computing. To address this, they proposed a conceptual framework that builds upon established high-performance computing concepts. Their analysis aimed to facilitate the integration according to the different workflows required for optimization, machine learning and simulation.Link: https://arxiv.org/abs/2308.06608

August 29, 2023

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