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Measurement-Induced Multimode Squeezed Light Interferometers with Scalable Architectures

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arXiv 2025年

作者： Verma, Abhinav Hastrup, Jacob Neergaard-Nielsen, Jonas S. Andersen, Ulrik L. Department of Physics Technical University of Denmark Fysikvej Kongens Lyngby 2800 Denmark Center for Quantum Devices and NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Denmark

In the rapidly expanding realm of photonic quantum information processing, the role of multimode squeezed light interferometers is critical. These devices are pivotal in enabling a wide range of applications, from quantum computing and sensing to advanced communication systems. Although linear interferometers with full programmability have been realized with up to 32 modes [1, 2], scaling to hundreds of modes is hampered by exponential increases in optical losses with circuit depth. Here we present and experimentally demonstrate highly scalable, low-loss multimode squeezed light interferometer schemes, capitalizing on measurement-induced operations and a shallow circuit approach. We validate our approach through a 6-mode interferometer and subsequently demonstrate its scalability by extending the design to 400 modes. This development marks a step toward realizing large-scale Noisy Intermediate-Scale quantum (NISQ) algorithm applications, employing shallow circuits and addressing the prevalent issue of optical losses in photonic quantum information processing. Copyright © 2025, The Authors. All rights reserved.

关键词： Squeezed light

Collective Formation of Misfit Dislocations at the Critical Thickness for Equilibrium Nanowire Heterostructures

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SSRN

SSRN 2023年

作者： Nikolajsen, Thue Christian Thann Krogstrup, Peter Schuwalow, Sergej Særkjær, Tobias Skov NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark Center for Quantum Devices Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark

In this work we model the evolution of strain energy during different growth stages of heterostructure nanowires. We find that the minimum energy configuration changes abruptly from fully elastically strained to partially relaxed due to collective formation of a misfit dislocation network. The transition at the critical thickness is associated with a characteristic density of *** insights are gained from a technique developed to simulate misfit dislocations in a finite element framework, incorporating both elastic and plastic relaxation. We argue that these results have general relevance for mismatched heterostructures. © 2023, The Authors. All rights reserved.

关键词： Crystal structure

Purifying Photon Indistinguishability through quantum Interference

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Physical Review Letters 2024年第3期133卷 033604-033604页

作者： Carlos F. D. Faurby Lorenzo Carosini Huan Cao Patrik I. Sund Lena M. Hansen Francesco Giorgino Andrew B. Villadsen Stefan N. van den Hoven Peter Lodahl Stefano Paesani Juan C. Loredo Philip Walther Center for Hybrid Quantum Networks (Hy-Q) Niels Bohr Institute Faculty of Physics Vienna Center for Quantum Science and Technology (VCQ) 1090 Vienna Austria Christian Doppler Laboratory for Photonic Quantum Computer Faculty of Physics MESA+ Institute for Nanotechnology NNF Quantum Computing Programme Niels Bohr Institute Research Network for Quantum Aspects of Space Time (TURIS) 1090 Vienna Austria Institute for Quantum Optics and Quantum Information (IQOQI) Vienna Austrian Academy of Sciences Vienna Austria

Indistinguishability between photons is a key requirement for scalable photonic quantum technologies. We experimentally demonstrate that partly distinguishable single photons can be purified to reach near-unity indistinguishability by the process of quantum interference with ancillary photons followed by heralded detection of a subset of them. We report on the indistinguishability of the purified photons by interfering two purified photons and show improvements in the photon indistinguishability of 2.774(3)% in the low-noise regime, and as high as 10.2(5)% in the high-noise regime.

关键词： quantum circuits quantum communication, protocols & technology quantum protocols quantum state engineering Single photon sources Optical interferometry

Self-correcting GKP qubit and gates in a driven-dissipative circuit

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arXiv 2024年

作者： Nathan, Frederik O’Brien, Liam Noh, Kyungjoo Matheny, Matthew H. Grimsmo, Arne L. Jiang, Liang Refael, Gil Center for Quantum Devices and NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark Department of Physics Institute for Quantum Information and Matter California Institute of Technology PasadenaCA91125 United States AWS Center for Quantum Computing PasadenaCA91125 United States Pritzker School of Molecular Engineering The University of Chicago ChicagoIL60637 United States

We propose a circuit architecture for a dissipatively error-corrected GKP qubit. The device consists of a high-impedance LC circuit coupled to a Josephson junction and a resistor via a controllable switch. When the switch is activated via a particular family of stepwise protocols, the resistor absorbs all noise-induced entropy, resulting in dissipative error correction of both phase and amplitude errors. This leads to an exponential increase of qubit lifetime, reaching beyond 10ms in simulations with near-feasible parameters. We show that the lifetime remains exponentially long in the presence of extrinsic noise and device/control imperfections (e.g., due to parasitics and finite control bandwidth) under specific thresholds. In this regime, lifetime is likely only limited by phase slips and quasiparticle tunneling. We show that the qubit can be read out and initialized via measurement of the supercurrent in the Josephson junction. We finally show that the qubit supports native self-correcting single-qubit Clifford gates, where dissipative error-correction of control noise leads to exponential suppression of gate infidelity. Copyright © 2024, The Authors. All rights reserved.

关键词： Resistors

Andreev spin relaxation time in a shadow-evaporated InAs weak link

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arXiv 2025年

作者： Lu, Haoran Bofill, David F. Sun, Zhenhai Kanne, Thomas Nygård, Jesper Kjaergaard, Morten Fatemi, Valla School of Applied and Engineering Physics Cornell University IthacaNY14853 United States Center for Quantum Devices Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark

Andreev spin qubits are a new qubit platform that merges superconductivity with semiconductor physics. The mechanisms dominating observed energy relaxation remain unidentified. We report here on three steps taken to address these questions in an InAs nanowire weak link. First, we designed a microwave readout circuit tuned to be directly sensitive to the spin-dependent inductance of the weak link so that higher orbital states are not necessary for readout – this resulted in larger windows in parameter space in which the spin state properties can be probed. Second, we implemented a successful gap-engineering strategy to mitigate quasiparticle poisoning. Third, the weak link was fabricated by in situ shadow evaporation, which has been shown to improve atomic-scale disorder. We show how our design allows characterization of the spin stability and coherence over the full range of magnetic flux and gate voltage of an odd parity bias point. The spin relaxation and dephasing rates are comparable with the best devices previously reported, suggestive that surface atomic-scale disorder and QP poisoning are not linked to spin relaxation in InAs nanowires. Our design strategies are transferrable to novel materials platforms for Andreev qubits such as germanium and carbon. © 2025, CC BY.

关键词： Nanowires

quantum Geometry and Bounds on Dissipation in Slowly Driven quantum Systems

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Physical Review Letters 2025年第14期134卷 146603-146603页

作者： Iliya Esin Étienne Lantagne-Hurtubise Frederik Nathan Gil Refael Department of Physics and Institute for Quantum Information and Matter California Institute of Technology Pasadena California 91125 USA Department of Physics Bar-Ilan University 52900 Ramat Gan Israel Département de Physique and Institut Quantique Université de Sherbrooke Sherbrooke Québec J1K 2R1 Canada Center for Quantum Devices and NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen 2100 Copenhagen Denmark

We show that energy dissipation in slowly driven, Markovian quantum systems at low temperature is linked to the geometry of the driving protocol through the quantum (or Fubini-Study) metric. Utilizing these findings, we establish lower bounds on dissipation rates in two-tone protocols, such as those employed for topological frequency conversion. Notably, in appropriate limits these bounds are only determined by the topology of the protocol and an effective quality factor of the system-bath coupling. Our results bridge topological and geometric phenomena with energy dissipation in open quantum systems, and further provide design principles for optimal driving protocols.

关键词： Topology

Hardware requirements for realizing a quantum advantage with deterministic single-photon sources

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Physical Review A 2024年第4期109卷 042613-042613页

作者： Patrik I. Sund Ravitej Uppu Stefano Paesani Peter Lodahl Center for Hybrid Quantum Networks (Hy-Q) Niels Bohr Institute University of Copenhagen Blegdamsvej 17 DK-2100 Copenhagen Denmark Department of Physics & Astronomy University of Iowa Iowa City Iowa 52242 USA NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Blegdamsvej 17 Copenhagen 2100 Denmark

Boson sampling is a specialized algorithm native to the quantum photonic platform developed for near-term demonstrations of quantum advantage over classical computers. While clear useful applications for such near-term pre-fault-tolerance devices are not currently known, reaching a quantum advantage regime serves as a useful benchmark for the hardware. Here, we analyze and detail hardware requirements needed to reach quantum advantage with deterministic quantum emitters, a promising platform for photonic quantum computing. We elucidate key steps that can be taken in experiments to overcome practical constraints and establish quantitative hardware-level requirements. We find that quantum advantage is within reach using quantum emitters with an efficiency of 60%–70% and interferometers constructed according to a hybrid-mode-encoding architecture, constituted of Mach-Zehnder interferometers with an insertion loss of 0.0035dB (a transmittance of 99.92%) per component.

关键词： Optical quantum information processing quantum algorithms & computation quantum benchmarking Single photon sources

A Digital quantum Algorithm for Non-Markovian Electron Transfer Dynamics Using Repeated Interactions

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arXiv 2025年

作者： Northcote, Lea K. Teynor, Matthew S. Solomon, Gemma C. NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Copenhagen ØDK-2100 Denmark Nano-Science Center Department of Chemistry University of Copenhagen Copenhagen ØDK-2100 Denmark

quantum algorithms have the potential to revolutionize our understanding of open quantum systems in chemistry. In this work, we demonstrate that quantum algorithms leveraging a repeated interaction model can effectively reproduce non-Markovian electron transfer processes under four different donor-acceptor parameter regimes and for a donor-bridge-acceptor system. We systematically explore how the algorithm scales for the regimes. Notably, our approach exhibits favorable scaling in the required repeated interaction length as the electronic coupling, temperature, damping rate, and system size increase. Furthermore, a single Trotter step per repeated interaction leads to an acceptably small error, and high-fidelity initial states can be prepared with a short time evolution. This efficiency highlights the potential of the algorithm for tackling increasingly complex systems. When fault-tolerant quantum hardware becomes available, the method could be extended to incorporate structured baths, additional energy levels, or more intricate coupling schemes, enabling the simulation of real-world open quantum systems that remain beyond the reach of classical computation. Copyright © 2025, The Authors. All rights reserved.

关键词： Markov processes

Superconducting Proximity Effect in Two-Dimensional Hole Gases

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arXiv 2024年

作者： Babkin, Serafim Joecker, Benjamin Flensberg, Karsten Serbyn, Maksym Danon, Jeroen Am Campus 1 Klosterneuburg3400 Austria Center for Quantum Devices Niels Bohr Institute University of Copenhagen CopenhagenDK-2100 Denmark NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Denmark Department of Physics Norwegian University of Science and Technology TrondheimNO-7491 Norway

Technology involving hybrid superconductor–semiconductor materials is a promising avenue for engineering quantum devices for information storage, manipulation, and transmission. Proximity-induced superconducting correlations are an essential part of such devices. While the proximity effect in the conduction band of common semiconductors is well understood, its manifestation in confined hole gases, realized for instance in germanium, is an active area of research. Lower-dimensional hole-based systems, particularly in germanium, are emerging as an attractive platform for a variety of solid-state quantum devices, due to their combination of efficient spin and charge control and long coherence times. The recent experimental realization of the proximity effect in germanium thus calls for a theoretical description that is tailored to hole gases. In this work, we propose a simple model to describe proximity-induced superconductivity in two-dimensional hole gases, incorporating both the heavy-hole (HH) and light-hole (LH) bands. We start from the Luttinger–Kohn model, introduce three parameters that characterize hopping across the superconductor–semiconductor interface, and derive explicit intraband and interband effective pairing terms for the HH and LH bands. Unlike previous approaches, our theory provides a quantitative relationship between induced pairings and interface properties. Restricting our general model to an experimentally relevant case where only the HH band crosses the chemical potential, we predict the coexistence of s-wave and d-wave singlet pairings, along with triplet-type pairings, and modified Zeeman and Rashba spin–orbit couplings. Our model thus presents a starting point for theoretical modeling of quantum devices based on proximitized hole gases, fueling further progress in quantum technology. Copyright © 2024, The Authors. All rights reserved.

关键词： Shear waves