Quantum state discrimination plays a central role in quantum information and communication. For the discrimination of optical quantum states, the two most widely adopted measurement techniques are photon detection, which produces discrete outcomes, and homodyne detection, which produces continuous outcomes. While various protocols using photon detection have been proposed for optimal and near-optimal discrimination between two coherent states, homodyne detection is known to have higher error rates, with its performance often referred to as the Gaussian limit. In this work, we demonstrate that, despite the fundamental differences between discretely labelled and continuously labelled measurements, continuously labelled non-Gaussian measurements can also achieve near-optimal coherent state discrimination. We explicitly design two coherent state discrimination protocols based on non-Gaussian unitary operations combined with homodyne detection and orthogonal polynomials, which surpass the Gaussian limit. Our results show that photon detection is not required for near-optimal coherent state discrimination and that we can achieve error rates close to the Helstrom bound at low energies with continuously labelled measurements. We also find that our schemes maintain an advantage over the photon detection-based Kennedy receiver for a moderate range of coherent state amplitudes.
{"title":"Near-optimal coherent state discrimination via continuously labelled non-Gaussian measurements","authors":"James Moran, Spiros Kechrimparis, Hyukjoon Kwon","doi":"arxiv-2409.08032","DOIUrl":"https://doi.org/arxiv-2409.08032","url":null,"abstract":"Quantum state discrimination plays a central role in quantum information and\u0000communication. For the discrimination of optical quantum states, the two most\u0000widely adopted measurement techniques are photon detection, which produces\u0000discrete outcomes, and homodyne detection, which produces continuous outcomes.\u0000While various protocols using photon detection have been proposed for optimal\u0000and near-optimal discrimination between two coherent states, homodyne detection\u0000is known to have higher error rates, with its performance often referred to as\u0000the Gaussian limit. In this work, we demonstrate that, despite the fundamental\u0000differences between discretely labelled and continuously labelled measurements,\u0000continuously labelled non-Gaussian measurements can also achieve near-optimal\u0000coherent state discrimination. We explicitly design two coherent state\u0000discrimination protocols based on non-Gaussian unitary operations combined with\u0000homodyne detection and orthogonal polynomials, which surpass the Gaussian\u0000limit. Our results show that photon detection is not required for near-optimal\u0000coherent state discrimination and that we can achieve error rates close to the\u0000Helstrom bound at low energies with continuously labelled measurements. We also\u0000find that our schemes maintain an advantage over the photon detection-based\u0000Kennedy receiver for a moderate range of coherent state amplitudes.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142202226","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ilhwan Kim, Yosep Kim, Yong-Su Kim, Kwang Jo Lee, Hyang-Tag Lim
Entangled photon sources are essential for quantum information applications, including quantum computation, quantum communication, and quantum metrology. Periodically poled (PP) crystals are commonly used to generate bright photon sources through quasi-phase matching. However, fabricating uniform micron-scale periodic structures poses significant technical difficulties, typically limiting the crystal thickness to less than a millimeter. Here, we adopt non-critical phase matching to produce a robust and bright polarization-entangled photon source based on a Sagnac interferometer. This method is tolerant of variations in pump incidence angles and temperature, and theoretically offers about a 2.5-fold brightness enhancement compared to quasi-phase matching. Additionally, the absence of periodic poling allows for a larger crystal cross-section. Using a bulk KTP crystal without a PP structure, we experimentally produce the four Bell states with a brightness of 25.1 kHz/mW, achieving purity, concurrence, and fidelity values close to 0.99. We believe our scheme will serve as a key building block for scalable and practical photonic quantum information applications.
{"title":"Robust and bright polarization-entangled photon sources exploiting non-critical phase matching without periodic poling","authors":"Ilhwan Kim, Yosep Kim, Yong-Su Kim, Kwang Jo Lee, Hyang-Tag Lim","doi":"arxiv-2409.07673","DOIUrl":"https://doi.org/arxiv-2409.07673","url":null,"abstract":"Entangled photon sources are essential for quantum information applications,\u0000including quantum computation, quantum communication, and quantum metrology.\u0000Periodically poled (PP) crystals are commonly used to generate bright photon\u0000sources through quasi-phase matching. However, fabricating uniform micron-scale\u0000periodic structures poses significant technical difficulties, typically\u0000limiting the crystal thickness to less than a millimeter. Here, we adopt\u0000non-critical phase matching to produce a robust and bright\u0000polarization-entangled photon source based on a Sagnac interferometer. This\u0000method is tolerant of variations in pump incidence angles and temperature, and\u0000theoretically offers about a 2.5-fold brightness enhancement compared to\u0000quasi-phase matching. Additionally, the absence of periodic poling allows for a\u0000larger crystal cross-section. Using a bulk KTP crystal without a PP structure,\u0000we experimentally produce the four Bell states with a brightness of 25.1\u0000kHz/mW, achieving purity, concurrence, and fidelity values close to 0.99. We\u0000believe our scheme will serve as a key building block for scalable and\u0000practical photonic quantum information applications.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142202259","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Manuel Calixto, Alberto Mayorgas, Octavio Castaños
Zero energy eigenstates $psi_0(theta)$ of the twisted bilayer graphene Hamiltonian at the Dirac point show a high sensitivity to the twist angle $theta$ near the magic angles where the effective Fermi velocity vanishes. We use information theory markers, like fidelity-susceptibility and entanglement entropy of the reduced density matrix to the layer sector, to capture this quantum criticality of zero modes at magic twist angles.
{"title":"Capturing magic angles in twisted bilayer graphene from information theory markers","authors":"Manuel Calixto, Alberto Mayorgas, Octavio Castaños","doi":"arxiv-2409.07935","DOIUrl":"https://doi.org/arxiv-2409.07935","url":null,"abstract":"Zero energy eigenstates $psi_0(theta)$ of the twisted bilayer graphene\u0000Hamiltonian at the Dirac point show a high sensitivity to the twist angle\u0000$theta$ near the magic angles where the effective Fermi velocity vanishes. We\u0000use information theory markers, like fidelity-susceptibility and entanglement\u0000entropy of the reduced density matrix to the layer sector, to capture this\u0000quantum criticality of zero modes at magic twist angles.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142202286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Seok-Hyung Lee, Felix Thomsen, Nicholas Fazio, Benjamin J. Brown, Stephen D. Bartlett
Fault-tolerant implementation of non-Clifford gates is a major challenge for achieving universal fault-tolerant quantum computing with quantum error-correcting codes. Magic state distillation is the most well-studied method for this but requires significant resources. Hence, it is crucial to tailor and optimize magic state distillation for specific codes from both logical- and physical-level perspectives. In this work, we perform such optimization for two-dimensional color codes, which are promising due to their higher encoding rates compared to surface codes, transversal implementation of Clifford gates, and efficient lattice surgery. We propose two distillation schemes based on the 15-to-1 distillation circuit and lattice surgery, which differ in their methods for handling faulty rotations. Our first scheme uses faulty T-measurement, offering resource efficiency when the target infidelity is above a certain threshold ($sim 35p^3$ for physical error rate $p$). To achieve lower infidelities while maintaining resource efficiency, our second scheme exploits a distillation-free fault-tolerant magic state preparation protocol, achieving significantly lower infidelities (e.g., $sim 10^{-19}$ for $p = 10^{-4}$) than the first scheme. Notably, our schemes outperform the best existing magic state distillation methods for color codes by up to about two orders of magnitude in resource costs for a given achievable target infidelity.
{"title":"Low-overhead magic state distillation with color codes","authors":"Seok-Hyung Lee, Felix Thomsen, Nicholas Fazio, Benjamin J. Brown, Stephen D. Bartlett","doi":"arxiv-2409.07707","DOIUrl":"https://doi.org/arxiv-2409.07707","url":null,"abstract":"Fault-tolerant implementation of non-Clifford gates is a major challenge for\u0000achieving universal fault-tolerant quantum computing with quantum\u0000error-correcting codes. Magic state distillation is the most well-studied\u0000method for this but requires significant resources. Hence, it is crucial to\u0000tailor and optimize magic state distillation for specific codes from both\u0000logical- and physical-level perspectives. In this work, we perform such\u0000optimization for two-dimensional color codes, which are promising due to their\u0000higher encoding rates compared to surface codes, transversal implementation of\u0000Clifford gates, and efficient lattice surgery. We propose two distillation\u0000schemes based on the 15-to-1 distillation circuit and lattice surgery, which\u0000differ in their methods for handling faulty rotations. Our first scheme uses\u0000faulty T-measurement, offering resource efficiency when the target infidelity\u0000is above a certain threshold ($sim 35p^3$ for physical error rate $p$). To\u0000achieve lower infidelities while maintaining resource efficiency, our second\u0000scheme exploits a distillation-free fault-tolerant magic state preparation\u0000protocol, achieving significantly lower infidelities (e.g., $sim 10^{-19}$ for\u0000$p = 10^{-4}$) than the first scheme. Notably, our schemes outperform the best\u0000existing magic state distillation methods for color codes by up to about two\u0000orders of magnitude in resource costs for a given achievable target infidelity.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142202289","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dipti Jasrasaria, Arkajit Mandal, David R. Reichman, Timothy C. Berkelbach
In this work we investigate anharmonic vibrational polaritons formed due to strong light-matter interactions in an optical cavity between radiation modes and anharmonic vibrations beyond the long-wavelength limit. We introduce a conceptually simple description of light-matter interactions, where spatially localized cavity radiation modes couple to localized vibrations. Within this theoretical framework, we employ self-consistent phonon theory and vibrational dynamical mean-field theory to efficiently simulate momentum-resolved vibrational-polariton spectra, including effects of anharmonicity. Numerical simulations in model systems demonstrate the accuracy and applicability of our approach.
{"title":"Simulating anharmonic vibrational polaritons beyond the long wavelength approximation","authors":"Dipti Jasrasaria, Arkajit Mandal, David R. Reichman, Timothy C. Berkelbach","doi":"arxiv-2409.07992","DOIUrl":"https://doi.org/arxiv-2409.07992","url":null,"abstract":"In this work we investigate anharmonic vibrational polaritons formed due to\u0000strong light-matter interactions in an optical cavity between radiation modes\u0000and anharmonic vibrations beyond the long-wavelength limit. We introduce a\u0000conceptually simple description of light-matter interactions, where spatially\u0000localized cavity radiation modes couple to localized vibrations. Within this\u0000theoretical framework, we employ self-consistent phonon theory and vibrational\u0000dynamical mean-field theory to efficiently simulate momentum-resolved\u0000vibrational-polariton spectra, including effects of anharmonicity. Numerical\u0000simulations in model systems demonstrate the accuracy and applicability of our\u0000approach.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142202229","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fadwa Benabdallah, M. Y. Abd-Rabbou, Mohammed Daoud, Saeed Haddadi
We explore the quantum information resources within bipartite pure and mixed states of the quantum spin-1 Heisenberg dimer system, considering some interesting factors such as the $l_{1}$-norm of quantum coherence, relative coherence, entanglement, and steering, influenced by the magnetic field and uniaxial single-ion anisotropy. Through a thorough investigation, we derive the system's density operator at thermal equilibrium and establish a mathematical framework for analyzing quantum correlation metrics. Our results unveil the system's behavior at absolute zero temperature, revealing quantum antiferromagnetic, ferromagnetic, and ferrimagnetic phase transitions governed by the magnetic field and anisotropy parameters. We further observe temperature's role in transitioning the system towards classical states, impacting coherence, entanglement, and steering differently. Notably, we find that increasing the exchange anisotropy parameter can reinforce quantum correlations while adjusting the uniaxial single-ion anisotropy parameter influences the system's quantumness, particularly when positive. Some recommendations to maximize quantum coherence, entanglement, and steering involve temperature reduction, increasing the exchange anisotropy parameter, and carefully managing the magnetic field and uniaxial single-ion anisotropy parameter, highlighting the intricate interplay between these factors in maintaining the system's quantum properties.
{"title":"Quantum Information Resources in Spin-1 Heisenberg Dimer Systems","authors":"Fadwa Benabdallah, M. Y. Abd-Rabbou, Mohammed Daoud, Saeed Haddadi","doi":"arxiv-2409.08082","DOIUrl":"https://doi.org/arxiv-2409.08082","url":null,"abstract":"We explore the quantum information resources within bipartite pure and mixed\u0000states of the quantum spin-1 Heisenberg dimer system, considering some\u0000interesting factors such as the $l_{1}$-norm of quantum coherence, relative\u0000coherence, entanglement, and steering, influenced by the magnetic field and\u0000uniaxial single-ion anisotropy. Through a thorough investigation, we derive the\u0000system's density operator at thermal equilibrium and establish a mathematical\u0000framework for analyzing quantum correlation metrics. Our results unveil the\u0000system's behavior at absolute zero temperature, revealing quantum\u0000antiferromagnetic, ferromagnetic, and ferrimagnetic phase transitions governed\u0000by the magnetic field and anisotropy parameters. We further observe\u0000temperature's role in transitioning the system towards classical states,\u0000impacting coherence, entanglement, and steering differently. Notably, we find\u0000that increasing the exchange anisotropy parameter can reinforce quantum\u0000correlations while adjusting the uniaxial single-ion anisotropy parameter\u0000influences the system's quantumness, particularly when positive. Some\u0000recommendations to maximize quantum coherence, entanglement, and steering\u0000involve temperature reduction, increasing the exchange anisotropy parameter,\u0000and carefully managing the magnetic field and uniaxial single-ion anisotropy\u0000parameter, highlighting the intricate interplay between these factors in\u0000maintaining the system's quantum properties.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142202246","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hasan Abbas Al-Mohammed, Saif Al-Kuwari, Hashir Kuniyil, Ahmed Farouk
Quantum Key Distribution (QKD) is a pivotal technology in the quest for secure communication, harnessing the power of quantum mechanics to ensure robust data protection. However, scaling QKD to meet the demands of high-speed, real-world applications remains a significant challenge. Traditional key rate determination methods, dependent on complex mathematical models, often fall short in efficiency and scalability. In this paper, we propose an approach that involves integrating machine learning (ML) techniques with the Cascade error correction protocol to enhance the scalability and efficiency of QKD systems. Our ML-based approach utilizes an autoencoder framework to predict the Quantum Bit Error Rate (QBER) and final key length with over 99% accuracy. This method significantly reduces error correction time, maintaining a consistently low computation time even with large input sizes, such as data rates up to 156 Mbps. In contrast, traditional methods exhibit exponentially increasing computation times as input sizes grow, highlighting the superior scalability of our ML-based solution. Through comprehensive simulations, we demonstrate that our method not only accelerates the error correction process but also optimizes resource utilization, making it more cost-effective and practical for real-world deployment. The Cascade protocol's integration further enhances system security by dynamically adjusting error correction based on real-time QBER observations, providing robust protection against potential eavesdropping. Our research establishes a new benchmark for scalable, high-throughput QKD systems, proving that machine learning can significantly advance the field of quantum cryptography. This work continues the evolution towards truly scalable quantum communication.
量子密钥分发（QKD）是实现安全通信的关键技术，它利用量子力学的力量确保数据得到可靠保护。然而，如何扩展 QKD 以满足高速实际应用的需求仍然是一项重大挑战。传统的密钥评级确定方法依赖于复杂的数学模型，在效率和可扩展性方面往往力不从心。在本文中，我们提出了一种将机器学习（ML）技术与级联纠错协议相结合的方法，以提高 QKD 系统的可扩展性和效率。我们基于 ML 的方法利用自动编码器框架来预测量子比特错误率（QBER）和最终密钥长度，准确率超过 99%。这种方法大大缩短了纠错时间，即使输入数据量很大，如数据传输速率高达 156Mbps，也能保持持续较低的计算时间。相比之下，传统方法的计算时间会随着输入大小的增加而呈指数级增长，这凸显了我们基于 ML 的解决方案优越的可扩展性。通过全面的仿真，我们证明了我们的方法不仅能加快纠错过程，还能优化资源利用率，使其在现实世界的部署中更具成本效益和实用性。Cascade 协议的集成可根据实时 QBER 观察结果动态调整纠错，从而进一步增强系统安全性，为防止潜在窃听提供了强有力的保护。我们的研究为可扩展、高吞吐量 QKD 系统确立了新的基准，证明机器学习可以极大地推动量子密码学领域的发展。这项工作将继续推动真正可扩展量子通信的发展。
{"title":"Towards Scalable Quantum Key Distribution: A Machine Learning-Based Cascade Protocol Approach","authors":"Hasan Abbas Al-Mohammed, Saif Al-Kuwari, Hashir Kuniyil, Ahmed Farouk","doi":"arxiv-2409.08038","DOIUrl":"https://doi.org/arxiv-2409.08038","url":null,"abstract":"Quantum Key Distribution (QKD) is a pivotal technology in the quest for\u0000secure communication, harnessing the power of quantum mechanics to ensure\u0000robust data protection. However, scaling QKD to meet the demands of high-speed,\u0000real-world applications remains a significant challenge. Traditional key rate\u0000determination methods, dependent on complex mathematical models, often fall\u0000short in efficiency and scalability. In this paper, we propose an approach that\u0000involves integrating machine learning (ML) techniques with the Cascade error\u0000correction protocol to enhance the scalability and efficiency of QKD systems.\u0000Our ML-based approach utilizes an autoencoder framework to predict the Quantum\u0000Bit Error Rate (QBER) and final key length with over 99% accuracy. This method\u0000significantly reduces error correction time, maintaining a consistently low\u0000computation time even with large input sizes, such as data rates up to 156\u0000Mbps. In contrast, traditional methods exhibit exponentially increasing\u0000computation times as input sizes grow, highlighting the superior scalability of\u0000our ML-based solution. Through comprehensive simulations, we demonstrate that\u0000our method not only accelerates the error correction process but also optimizes\u0000resource utilization, making it more cost-effective and practical for\u0000real-world deployment. The Cascade protocol's integration further enhances\u0000system security by dynamically adjusting error correction based on real-time\u0000QBER observations, providing robust protection against potential eavesdropping. Our research establishes a new benchmark for scalable, high-throughput QKD\u0000systems, proving that machine learning can significantly advance the field of\u0000quantum cryptography. This work continues the evolution towards truly scalable\u0000quantum communication.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142202253","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cryogenic quantum computers play a leading role in demonstrating quantum advantage. Given the severe constraints on the cooling capacity in cryogenic environments, thermal design is crucial for the scalability of these computers. The sources of heat dissipation include passive inflow via inter-temperature wires and the power consumption of components located in the cryostat, such as wire amplifiers and quantum-classical interfaces. Thus, a critical challenge is to reduce the number of wires by reducing the required inter-temperature bandwidth while maintaining minimal additional power consumption in the cryostat. One solution to address this challenge is near-data processing using ultra-low-power computational logic within the cryostat. Based on the workload analysis and domain-specific system design focused on Variational Quantum Algorithms (VQAs), we propose the Cryogenic Counter-based Co-processor for VQAs (C3-VQA) to enhance the design scalability of cryogenic quantum computers under the thermal constraint. The C3-VQA utilizes single-flux-quantum logic, which is an ultra-low-power superconducting digital circuit that operates at the 4 K environment. The C3-VQA precomputes a part of the expectation value calculations for VQAs and buffers intermediate values using simple bit operation units and counters in the cryostat, thereby reducing the required inter-temperature bandwidth with small additional power consumption. Consequently, the C3-VQA reduces the number of wires, leading to a reduction in the total heat dissipation in the cryostat. Our evaluation shows that the C3-VQA reduces the total heat dissipation at the 4 K stage by 30% and 81% under sequential-shot and parallel-shot execution scenarios, respectively. Furthermore, a case study in quantum chemistry shows that the C3-VQA reduces total heat dissipation by 87% with a 10,000-qubit system.
{"title":"C3-VQA: Cryogenic Counter-based Co-processor for Variational Quantum Algorithms","authors":"Yosuke Ueno, Satoshi Imamura, Yuna Tomida, Teruo Tanimoto, Masamitsu Tanaka, Yutaka Tabuchi, Koji Inoue, Hiroshi Nakamura","doi":"arxiv-2409.07847","DOIUrl":"https://doi.org/arxiv-2409.07847","url":null,"abstract":"Cryogenic quantum computers play a leading role in demonstrating quantum\u0000advantage. Given the severe constraints on the cooling capacity in cryogenic\u0000environments, thermal design is crucial for the scalability of these computers.\u0000The sources of heat dissipation include passive inflow via inter-temperature\u0000wires and the power consumption of components located in the cryostat, such as\u0000wire amplifiers and quantum-classical interfaces. Thus, a critical challenge is\u0000to reduce the number of wires by reducing the required inter-temperature\u0000bandwidth while maintaining minimal additional power consumption in the\u0000cryostat. One solution to address this challenge is near-data processing using\u0000ultra-low-power computational logic within the cryostat. Based on the workload\u0000analysis and domain-specific system design focused on Variational Quantum\u0000Algorithms (VQAs), we propose the Cryogenic Counter-based Co-processor for VQAs\u0000(C3-VQA) to enhance the design scalability of cryogenic quantum computers under\u0000the thermal constraint. The C3-VQA utilizes single-flux-quantum logic, which is\u0000an ultra-low-power superconducting digital circuit that operates at the 4 K\u0000environment. The C3-VQA precomputes a part of the expectation value\u0000calculations for VQAs and buffers intermediate values using simple bit\u0000operation units and counters in the cryostat, thereby reducing the required\u0000inter-temperature bandwidth with small additional power consumption.\u0000Consequently, the C3-VQA reduces the number of wires, leading to a reduction in\u0000the total heat dissipation in the cryostat. Our evaluation shows that the\u0000C3-VQA reduces the total heat dissipation at the 4 K stage by 30% and 81% under\u0000sequential-shot and parallel-shot execution scenarios, respectively.\u0000Furthermore, a case study in quantum chemistry shows that the C3-VQA reduces\u0000total heat dissipation by 87% with a 10,000-qubit system.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142202254","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Huan-Yu Wang, Ji Li, Wu-Ming Liu, Lin Wen, Xiao-Fei Zhang
We investigate the localization behavior of two-body Hubbard model in the presence of non-reciprocal tunneling, where the interaction induced Anderson localization competes with the non-Hermitian skin effects and gives rise to diverse patterns of density profiles. Here, we present the non-Hermitian bound states obtained with the center of mass methods in the conditions of strong repulsive interaction, where a faded diagonal line localization is observed. While for the continuum limit, the non-Hermitian skin effects are manifested by non-zero windings of the eigen-energy spectrum. For the moderate interaction strength, it is illustrated that the system possesses multiple Lyapunov exponents due to the competence above and as a consequence, in sharp contrast to the corner localization, the two-body non-Hermitian continuum states can exhibit multiple localization center. By further including two-photon tunneling, topological nontrivial photon bound pairs can be obtained. Finally, the experimental simulations are proposed based on the platforms of the electrical circuit lattices.
{"title":"Exotic localization for the two body bound states in the non-reciprocal Hubbard model","authors":"Huan-Yu Wang, Ji Li, Wu-Ming Liu, Lin Wen, Xiao-Fei Zhang","doi":"arxiv-2409.07883","DOIUrl":"https://doi.org/arxiv-2409.07883","url":null,"abstract":"We investigate the localization behavior of two-body Hubbard model in the\u0000presence of non-reciprocal tunneling, where the interaction induced Anderson\u0000localization competes with the non-Hermitian skin effects and gives rise to\u0000diverse patterns of density profiles. Here, we present the non-Hermitian bound\u0000states obtained with the center of mass methods in the conditions of strong\u0000repulsive interaction, where a faded diagonal line localization is observed.\u0000While for the continuum limit, the non-Hermitian skin effects are manifested by\u0000non-zero windings of the eigen-energy spectrum. For the moderate interaction\u0000strength, it is illustrated that the system possesses multiple Lyapunov\u0000exponents due to the competence above and as a consequence, in sharp contrast\u0000to the corner localization, the two-body non-Hermitian continuum states can\u0000exhibit multiple localization center. By further including two-photon\u0000tunneling, topological nontrivial photon bound pairs can be obtained. Finally,\u0000the experimental simulations are proposed based on the platforms of the\u0000electrical circuit lattices.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142202250","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Alessandro Laneve, Michele B. Rota, Francesco Basso Basset, Mattia Beccaceci, Valerio Villari, Thomas Oberleitner, Yorick Reum, Tobias M. Krieger, Quirin Buchinger, Saimon F. Covre da Silva, Andreas Pfenning, Sandra Stroj, Sven Höfling, Armando Rastelli, Tobias Huber-Loyola, Rinaldo Trotta
The generation of entangled photons from radiative cascades has enabled milestone experiments in quantum information science with several applications in photonic quantum technologies. Significant efforts are being devoted to pushing the performances of near-deterministic entangled-photon sources based on single quantum emitters often embedded in photonic cavities, so to boost the flux of photon pairs. The general postulate is that the emitter generates photons in a nearly maximally entangled state of polarization, ready for application purposes. Here, we demonstrate that this assumption is unjustified. We show that in radiative cascades there exists an interplay between photon polarization and emission wavevector, strongly affecting quantum correlations when emitters are embedded in micro-cavities. We discuss how the polarization entanglement of photon pairs from a biexciton-exciton cascade in quantum dots strongly depends on their propagation wavevector, and it can even vanish for large emission angles. Our experimental results, backed by theoretical modelling, yield a brand-new understanding of cascaded emission for various quantum emitters. In addition, our model provides quantitative guidelines for designing optical microcavities that retain both a high degree of entanglement and collection efficiency, moving the community one step further towards an ideal source of entangled photons for quantum technologies.
{"title":"Wavevector-resolved polarization entanglement from radiative cascades","authors":"Alessandro Laneve, Michele B. Rota, Francesco Basso Basset, Mattia Beccaceci, Valerio Villari, Thomas Oberleitner, Yorick Reum, Tobias M. Krieger, Quirin Buchinger, Saimon F. Covre da Silva, Andreas Pfenning, Sandra Stroj, Sven Höfling, Armando Rastelli, Tobias Huber-Loyola, Rinaldo Trotta","doi":"arxiv-2409.07875","DOIUrl":"https://doi.org/arxiv-2409.07875","url":null,"abstract":"The generation of entangled photons from radiative cascades has enabled\u0000milestone experiments in quantum information science with several applications\u0000in photonic quantum technologies. Significant efforts are being devoted to\u0000pushing the performances of near-deterministic entangled-photon sources based\u0000on single quantum emitters often embedded in photonic cavities, so to boost the\u0000flux of photon pairs. The general postulate is that the emitter generates\u0000photons in a nearly maximally entangled state of polarization, ready for\u0000application purposes. Here, we demonstrate that this assumption is unjustified.\u0000We show that in radiative cascades there exists an interplay between photon\u0000polarization and emission wavevector, strongly affecting quantum correlations\u0000when emitters are embedded in micro-cavities. We discuss how the polarization\u0000entanglement of photon pairs from a biexciton-exciton cascade in quantum dots\u0000strongly depends on their propagation wavevector, and it can even vanish for\u0000large emission angles. Our experimental results, backed by theoretical\u0000modelling, yield a brand-new understanding of cascaded emission for various\u0000quantum emitters. In addition, our model provides quantitative guidelines for\u0000designing optical microcavities that retain both a high degree of entanglement\u0000and collection efficiency, moving the community one step further towards an\u0000ideal source of entangled photons for quantum technologies.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142202252","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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