Pub Date : 2025-02-28DOI: 10.1088/2058-9565/adaedf
Chris Gustin, Ryotatsu Yanagimoto, Edwin Ng, Tatsuhiro Onodera and Hideo Mabuchi
In broadband quantum optical systems, nonlinear interactions among a large number of frequency components induce complex dynamics that may defy heuristic analysis. In this work we introduce a perturbative framework for factoring out reservoir degrees of freedom and establishing a concise effective model (effective field theory) for the remaining system. Our approach combines approximate diagonalization of judiciously partitioned subsystems with master equation techniques. We consider cascaded optical (quadratic) nonlinearities as an example and show that the dynamics can be construed (to leading order) as self-phase modulations of dressed fundamental modes plus cross-phase modulations of dressed fundamental and second-harmonic modes. We then formally eliminate the second-harmonic degrees of freedom and identify emergent features of the fundamental wave dynamics, such as two-photon loss channels, and examine conditions for accuracy of the reduced model in dispersive and dissipative parameter regimes. Our results highlight the utility of system-reservoir methods for deriving accurate, intuitive reduced models for complex dynamics in broadband nonlinear quantum photonics, and may help guide quantum technological proposals in emerging systems where quantum effects become significant at the single-photon level.
{"title":"Effective field theories in broadband quantum optics: modeling phase modulation and two-photon loss from cascaded quadratic nonlinearities","authors":"Chris Gustin, Ryotatsu Yanagimoto, Edwin Ng, Tatsuhiro Onodera and Hideo Mabuchi","doi":"10.1088/2058-9565/adaedf","DOIUrl":"https://doi.org/10.1088/2058-9565/adaedf","url":null,"abstract":"In broadband quantum optical systems, nonlinear interactions among a large number of frequency components induce complex dynamics that may defy heuristic analysis. In this work we introduce a perturbative framework for factoring out reservoir degrees of freedom and establishing a concise effective model (effective field theory) for the remaining system. Our approach combines approximate diagonalization of judiciously partitioned subsystems with master equation techniques. We consider cascaded optical (quadratic) nonlinearities as an example and show that the dynamics can be construed (to leading order) as self-phase modulations of dressed fundamental modes plus cross-phase modulations of dressed fundamental and second-harmonic modes. We then formally eliminate the second-harmonic degrees of freedom and identify emergent features of the fundamental wave dynamics, such as two-photon loss channels, and examine conditions for accuracy of the reduced model in dispersive and dissipative parameter regimes. Our results highlight the utility of system-reservoir methods for deriving accurate, intuitive reduced models for complex dynamics in broadband nonlinear quantum photonics, and may help guide quantum technological proposals in emerging systems where quantum effects become significant at the single-photon level.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"27 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2025-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143517945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-27DOI: 10.1088/2058-9565/adb781
Stefano Barison, Javier Robledo Moreno and Mario Motta
The simulation of molecular electronic structure is an important application of quantum devices. Recently, it has been shown that quantum devices can be effectively combined with classical supercomputing centers in the context of the sample-based quantum diagonalization (SQD) algorithm. This allowed the largest electronic structure quantum simulation to date (77 qubits) and opened near-term devices to practical use cases in chemistry toward the hundred-qubit mark. However, the description of many important physical and chemical properties of those systems, such as photo-absorption/-emission, requires a treatment that goes beyond the ground state alone. In this work, we extend the SQD algorithm to determine low-lying molecular excited states. The extended-SQD method improves over the original SQD method in accuracy, at the cost of an additional computational step. It also improves over quantum subspace expansion based on single and double electronic excitations, a widespread approach to excited states on pre-fault-tolerant quantum devices, in both accuracy and efficiency. We employ the extended SQD method to compute the first singlet (S1) and triplet (T1) excited states of the nitrogen molecule with a correlation-consistent basis set, and the ground- and excited-state properties of the [2Fe-2S] cluster.
{"title":"Quantum-centric computation of molecular excited states with extended sample-based quantum diagonalization","authors":"Stefano Barison, Javier Robledo Moreno and Mario Motta","doi":"10.1088/2058-9565/adb781","DOIUrl":"https://doi.org/10.1088/2058-9565/adb781","url":null,"abstract":"The simulation of molecular electronic structure is an important application of quantum devices. Recently, it has been shown that quantum devices can be effectively combined with classical supercomputing centers in the context of the sample-based quantum diagonalization (SQD) algorithm. This allowed the largest electronic structure quantum simulation to date (77 qubits) and opened near-term devices to practical use cases in chemistry toward the hundred-qubit mark. However, the description of many important physical and chemical properties of those systems, such as photo-absorption/-emission, requires a treatment that goes beyond the ground state alone. In this work, we extend the SQD algorithm to determine low-lying molecular excited states. The extended-SQD method improves over the original SQD method in accuracy, at the cost of an additional computational step. It also improves over quantum subspace expansion based on single and double electronic excitations, a widespread approach to excited states on pre-fault-tolerant quantum devices, in both accuracy and efficiency. We employ the extended SQD method to compute the first singlet (S1) and triplet (T1) excited states of the nitrogen molecule with a correlation-consistent basis set, and the ground- and excited-state properties of the [2Fe-2S] cluster.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"21 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143506813","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-21DOI: 10.1088/2058-9565/adb176
Jonathan Frazer, Takafumi Ono and Jonathan C F Matthews
Low loss and high-speed processing of photons is important to photonic quantum information technologies. The speed with which quantum light generation can be modulated impacts the clock rate of photonic quantum computers, the data rate of quantum communication and applications of quantum enhanced radio-frequency sensors. Here we use lossy carrier depletion modulators in a silicon waveguide nonlinear interferometer to modulate photon pair generation probability at 1 gigahertz (GHz) without exposing the generated photons to the phase dependent parasitic loss of the modulators. The super sensitivity of nonlinear interferometers reduces power consumption compared to modulating the driving laser. This can be used for high-speed programmable nonlinearity in waveguide networks for quantum technologies and for optical quantum sensors.
{"title":"A Gigahertz configurable silicon photonic integrated circuit nonlinear interferometer","authors":"Jonathan Frazer, Takafumi Ono and Jonathan C F Matthews","doi":"10.1088/2058-9565/adb176","DOIUrl":"https://doi.org/10.1088/2058-9565/adb176","url":null,"abstract":"Low loss and high-speed processing of photons is important to photonic quantum information technologies. The speed with which quantum light generation can be modulated impacts the clock rate of photonic quantum computers, the data rate of quantum communication and applications of quantum enhanced radio-frequency sensors. Here we use lossy carrier depletion modulators in a silicon waveguide nonlinear interferometer to modulate photon pair generation probability at 1 gigahertz (GHz) without exposing the generated photons to the phase dependent parasitic loss of the modulators. The super sensitivity of nonlinear interferometers reduces power consumption compared to modulating the driving laser. This can be used for high-speed programmable nonlinearity in waveguide networks for quantum technologies and for optical quantum sensors.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"24 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462833","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-21DOI: 10.1088/2058-9565/adb3c5
Mohammad Haidar, Olivier Adjoua, Siwar Badreddine, Alberto Peruzzo and Jean-Philip Piquemal
Due to their non-iterative nature, fixed unitary coupled cluster (UCC) ansätze are attractive for performing quantum chemistry variational quantum eigensolver (VQE) computations as they avoid pre-circuit measurements on a quantum computer. However, achieving chemical accuracy for strongly correlated systems with UCC requires further inclusion of higher-order fermionic excitations beyond triples increasing circuit depth. We introduce k-non-iterative disentangled unitary coupled cluster (NI-DUCC), a fixed and non-iterative disentangled UCC compact ansatz, based on specific ‘k’ sets of ‘qubit’ excitations, eliminating the needs for fermionic-type excitations. These elements scale linearly ( ) by leveraging Lie algebraic structures, with n being the number of qubits. The key excitations are screened through specific selection criteria, including the enforcement of all symmetries, to ensure the construction of a robust set of generators. NI-DUCC employs ‘k’ products of the exponential of - anti-Hermitian Pauli operators, where each single Pauli string has a length p. This results in a fewer two-qubit CNOT gates circuit scaling, , suitable for hardware implementations. Tested on LiH, H6 and BeH2, NI-DUCC-VQE achieves both chemical accuracy and rapid convergence even for molecules deviating significantly from equilibrium. It is hardware-efficient, reaching the exact full configuration interaction energy solution at specific layers, while reducing significantly the VQE optimization steps. NI-DUCC-VQE effectively addresses the gradient measurement bottleneck of ADAPT-VQE-like iterative algorithms, yet the classical computational cost of constructing the set of excitations increases exponentially with the number of qubits. We provide a first implementation for constructing the generators’ set, able to handle up to 20 qubits and discuss the efficiency perspectives.
{"title":"Non-iterative disentangled unitary coupled-cluster based on lie-algebraic structure","authors":"Mohammad Haidar, Olivier Adjoua, Siwar Badreddine, Alberto Peruzzo and Jean-Philip Piquemal","doi":"10.1088/2058-9565/adb3c5","DOIUrl":"https://doi.org/10.1088/2058-9565/adb3c5","url":null,"abstract":"Due to their non-iterative nature, fixed unitary coupled cluster (UCC) ansätze are attractive for performing quantum chemistry variational quantum eigensolver (VQE) computations as they avoid pre-circuit measurements on a quantum computer. However, achieving chemical accuracy for strongly correlated systems with UCC requires further inclusion of higher-order fermionic excitations beyond triples increasing circuit depth. We introduce k-non-iterative disentangled unitary coupled cluster (NI-DUCC), a fixed and non-iterative disentangled UCC compact ansatz, based on specific ‘k’ sets of ‘qubit’ excitations, eliminating the needs for fermionic-type excitations. These elements scale linearly ( ) by leveraging Lie algebraic structures, with n being the number of qubits. The key excitations are screened through specific selection criteria, including the enforcement of all symmetries, to ensure the construction of a robust set of generators. NI-DUCC employs ‘k’ products of the exponential of - anti-Hermitian Pauli operators, where each single Pauli string has a length p. This results in a fewer two-qubit CNOT gates circuit scaling, , suitable for hardware implementations. Tested on LiH, H6 and BeH2, NI-DUCC-VQE achieves both chemical accuracy and rapid convergence even for molecules deviating significantly from equilibrium. It is hardware-efficient, reaching the exact full configuration interaction energy solution at specific layers, while reducing significantly the VQE optimization steps. NI-DUCC-VQE effectively addresses the gradient measurement bottleneck of ADAPT-VQE-like iterative algorithms, yet the classical computational cost of constructing the set of excitations increases exponentially with the number of qubits. We provide a first implementation for constructing the generators’ set, able to handle up to 20 qubits and discuss the efficiency perspectives.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"22 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462832","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-21DOI: 10.1088/2058-9565/adb2be
Adnan A E Hajomer, Ulrik L Andersen and Tobias Gehring
Building scalable and secure quantum networks requires advanced quantum key distribution (QKD) protocols that support multi-user connectivity. Continuous-variable (CV) measurement-device-independent (MDI) QKD, which eliminates all detector side-channel attacks, is a promising candidate for creating various quantum network topologies-such as quantum access networks and star-type topologies-using standard technology and providing high secure key rates. However, its security has so far only been experimentally demonstrated in asymptotic regimes with limited secret key rates and complex experimental setups, limiting its practical applications. Here, we report an experimental validation of a CV MDI-QKD system, achieving a secure key rate of 2.6 Mbit s−1 against collective attacks in the finite-size regime over a 10 km fiber link. This is achieved using a new system design, incorporating a locally generated local oscillator, a new relay structure, a real-time phase locking system, and a well-designed digital-signal-processing pipeline for quantum state preparation and CV Bell measurements at a symbol rate of 20 MBaud. Our results set a new benchmark for secure key exchange and open the possibility of establishing high-performance CV MDI-QKD networks, paving the way toward a scalable quantum network.
{"title":"High-rate continuous-variable measurement device-independent quantum key distribution with finite-size security","authors":"Adnan A E Hajomer, Ulrik L Andersen and Tobias Gehring","doi":"10.1088/2058-9565/adb2be","DOIUrl":"https://doi.org/10.1088/2058-9565/adb2be","url":null,"abstract":"Building scalable and secure quantum networks requires advanced quantum key distribution (QKD) protocols that support multi-user connectivity. Continuous-variable (CV) measurement-device-independent (MDI) QKD, which eliminates all detector side-channel attacks, is a promising candidate for creating various quantum network topologies-such as quantum access networks and star-type topologies-using standard technology and providing high secure key rates. However, its security has so far only been experimentally demonstrated in asymptotic regimes with limited secret key rates and complex experimental setups, limiting its practical applications. Here, we report an experimental validation of a CV MDI-QKD system, achieving a secure key rate of 2.6 Mbit s−1 against collective attacks in the finite-size regime over a 10 km fiber link. This is achieved using a new system design, incorporating a locally generated local oscillator, a new relay structure, a real-time phase locking system, and a well-designed digital-signal-processing pipeline for quantum state preparation and CV Bell measurements at a symbol rate of 20 MBaud. Our results set a new benchmark for secure key exchange and open the possibility of establishing high-performance CV MDI-QKD networks, paving the way toward a scalable quantum network.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"18 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462824","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-19DOI: 10.1088/2058-9565/adb0e9
Jake Xuereb, Tiago Debarba, Marcus Huber and Paul Erker
Quantum direct coding or Schumacher compression generalised the ideas of Shannon theory, gave an operational meaning to the von Neumann entropy and established the term qubit. But remembering that information processing is carried out by physical processes prompts one to wonder what thermodynamic resources are required to compress quantum information and how they constrain one’s ability to perform this task. That is, if Alice and Bob only have access to thermal quantum states and clocks with finite accuracy, how well can they measure, encode and decode pure quantum state messages? In this work we examine these questions by modeling Alice’s typical measurement as a unitary involving a measurement probe, investigating imperfect timekeeping on encoding and decoding and considering the role of temperature in Bob’s appended qubits. In doing so, we derive fidelity bounds for this protocol involving the correlations Alice can form with their measurement probe, the variance of the clock’s ticks and the temperature of Bob’s qubits. Finally, we give an insight into the entropy produced by these two agents throughout the compression protocol by relating the resources they use to a quantum thermodynamic cooling protocol.
{"title":"Quantum coding with finite thermodynamic resources","authors":"Jake Xuereb, Tiago Debarba, Marcus Huber and Paul Erker","doi":"10.1088/2058-9565/adb0e9","DOIUrl":"https://doi.org/10.1088/2058-9565/adb0e9","url":null,"abstract":"Quantum direct coding or Schumacher compression generalised the ideas of Shannon theory, gave an operational meaning to the von Neumann entropy and established the term qubit. But remembering that information processing is carried out by physical processes prompts one to wonder what thermodynamic resources are required to compress quantum information and how they constrain one’s ability to perform this task. That is, if Alice and Bob only have access to thermal quantum states and clocks with finite accuracy, how well can they measure, encode and decode pure quantum state messages? In this work we examine these questions by modeling Alice’s typical measurement as a unitary involving a measurement probe, investigating imperfect timekeeping on encoding and decoding and considering the role of temperature in Bob’s appended qubits. In doing so, we derive fidelity bounds for this protocol involving the correlations Alice can form with their measurement probe, the variance of the clock’s ticks and the temperature of Bob’s qubits. Finally, we give an insight into the entropy produced by these two agents throughout the compression protocol by relating the resources they use to a quantum thermodynamic cooling protocol.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"15 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2025-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143443274","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-18DOI: 10.1088/2058-9565/adb3c6
Miguel Casanova, Kentaro Ohki and Francesco Ticozzi
We propose a novel optimization scheme designed to find optimally correctable subspace codes for a known quantum noise channel. To each candidate subspace code we first associate a universal recovery map, as if the code was perfectly correctable, and aim to maximize a performance functional that combines a modified channel fidelity with a tuneable regularization term that promotes simpler codes. With this choice optimization is performed only over the set of codes, and not over the set of recovery operators. The set of codes of fixed dimension is parametrized as a complex-valued Stiefel manifold: the resulting non-convex optimization problem is then solved by gradient-based local algorithms. When perfectly correctable codes cannot be found, a second optimization routine is run on the recovery Kraus map, also parametrized in a suitable Stiefel manifold via Stinespring representation. To test the approach, correctable codes are sought in different scenarios and compared to existing ones: three qubits subjected to bit-flip errors (single and correlated), four qubits undergoing local amplitude damping and five qubits subjected to local depolarizing channels. Approximate codes are found and tested for the previous examples as well pure non-Markovian dephasing noise acting on a spin, induced by a spin bath, and the noise of the first three qubits of IBM’s ibm_kyoto quantum computer. The fidelity results are competitive with existing iterative optimization algorithms, with respect to which we maintain a strong computational advantage, while obtaining simpler codes.
{"title":"Finding quantum codes via Riemannian optimization","authors":"Miguel Casanova, Kentaro Ohki and Francesco Ticozzi","doi":"10.1088/2058-9565/adb3c6","DOIUrl":"https://doi.org/10.1088/2058-9565/adb3c6","url":null,"abstract":"We propose a novel optimization scheme designed to find optimally correctable subspace codes for a known quantum noise channel. To each candidate subspace code we first associate a universal recovery map, as if the code was perfectly correctable, and aim to maximize a performance functional that combines a modified channel fidelity with a tuneable regularization term that promotes simpler codes. With this choice optimization is performed only over the set of codes, and not over the set of recovery operators. The set of codes of fixed dimension is parametrized as a complex-valued Stiefel manifold: the resulting non-convex optimization problem is then solved by gradient-based local algorithms. When perfectly correctable codes cannot be found, a second optimization routine is run on the recovery Kraus map, also parametrized in a suitable Stiefel manifold via Stinespring representation. To test the approach, correctable codes are sought in different scenarios and compared to existing ones: three qubits subjected to bit-flip errors (single and correlated), four qubits undergoing local amplitude damping and five qubits subjected to local depolarizing channels. Approximate codes are found and tested for the previous examples as well pure non-Markovian dephasing noise acting on a spin, induced by a spin bath, and the noise of the first three qubits of IBM’s ibm_kyoto quantum computer. The fidelity results are competitive with existing iterative optimization algorithms, with respect to which we maintain a strong computational advantage, while obtaining simpler codes.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"3 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435048","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-18DOI: 10.1088/2058-9565/adb3c7
Rod Rofougaran, Ralph Wang, Akshay Ajagekar and Fengqi You
Quantum computing holds transformative potential for various domains including cheminformatics through advancements in quantum algorithms. The key to realizing improvements with quantum algorithms in cheminformatics is encoding chemical data like proteins as quantum states with quantum state preparation. In this work, we propose a computational framework to encode proteins as quantum states for efficient downstream quantum processing. Protein data representations are encoded as multi-qubit quantum states with iterative quantum sparse state preparation guided by the classical heuristic search method for optimal gate sequence identification. The validity and efficiency of the proposed method is demonstrated with various computational experiments to encode uniform random states as well as proteins. Several performance comparisons against the baselines of exact and variational state preparation methods, the proposed approach is able to encode proteins with 25% fewer controlled-NOT gates while performing orders of magnitude faster than the variational method.
{"title":"Encoding proteins as quantum states with approximate quantum state preparation by iterated sparse state preparation","authors":"Rod Rofougaran, Ralph Wang, Akshay Ajagekar and Fengqi You","doi":"10.1088/2058-9565/adb3c7","DOIUrl":"https://doi.org/10.1088/2058-9565/adb3c7","url":null,"abstract":"Quantum computing holds transformative potential for various domains including cheminformatics through advancements in quantum algorithms. The key to realizing improvements with quantum algorithms in cheminformatics is encoding chemical data like proteins as quantum states with quantum state preparation. In this work, we propose a computational framework to encode proteins as quantum states for efficient downstream quantum processing. Protein data representations are encoded as multi-qubit quantum states with iterative quantum sparse state preparation guided by the classical heuristic search method for optimal gate sequence identification. The validity and efficiency of the proposed method is demonstrated with various computational experiments to encode uniform random states as well as proteins. Several performance comparisons against the baselines of exact and variational state preparation methods, the proposed approach is able to encode proteins with 25% fewer controlled-NOT gates while performing orders of magnitude faster than the variational method.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"11 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435049","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-18DOI: 10.1088/2058-9565/adb2bd
Guangze Chen and Anton Frisk Kockum
Open quantum many-body systems are of both fundamental and applicational interest. However, it remains an open challenge to simulate and solve such systems, both with state-of-the-art classical methods and with quantum-simulation protocols. To overcome this challenge, we introduce a simulator for open quantum many-body systems based on giant atoms, i.e. atoms (possibly artificial), that couple to a waveguide at multiple points, which can be wavelengths apart. We first show that a simulator consisting of two giant atoms can simulate the dynamics of two coupled qubits, where one qubit is subject to different drive amplitudes and dissipation rates. This simulation enables characterizing the quantum Zeno crossover in this model. We further show that by equipping the simulator with post-selection, it becomes possible to simulate the effective non-Hermitian Hamiltonian dynamics of the system and thereby characterize the transition from oscillatory to non-oscillatory dynamics due to varying dissipation rates. We demonstrate and analyze the robustness of these simulation results against noise affecting the giant atoms. Finally, we discuss and show how giant-atom-based simulators can be scaled up for digital–analog simulation of large open quantum many-body systems, e.g. generic dissipative spin models.
{"title":"Simulating open quantum systems with giant atoms","authors":"Guangze Chen and Anton Frisk Kockum","doi":"10.1088/2058-9565/adb2bd","DOIUrl":"https://doi.org/10.1088/2058-9565/adb2bd","url":null,"abstract":"Open quantum many-body systems are of both fundamental and applicational interest. However, it remains an open challenge to simulate and solve such systems, both with state-of-the-art classical methods and with quantum-simulation protocols. To overcome this challenge, we introduce a simulator for open quantum many-body systems based on giant atoms, i.e. atoms (possibly artificial), that couple to a waveguide at multiple points, which can be wavelengths apart. We first show that a simulator consisting of two giant atoms can simulate the dynamics of two coupled qubits, where one qubit is subject to different drive amplitudes and dissipation rates. This simulation enables characterizing the quantum Zeno crossover in this model. We further show that by equipping the simulator with post-selection, it becomes possible to simulate the effective non-Hermitian Hamiltonian dynamics of the system and thereby characterize the transition from oscillatory to non-oscillatory dynamics due to varying dissipation rates. We demonstrate and analyze the robustness of these simulation results against noise affecting the giant atoms. Finally, we discuss and show how giant-atom-based simulators can be scaled up for digital–analog simulation of large open quantum many-body systems, e.g. generic dissipative spin models.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"24 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435054","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-12DOI: 10.1088/2058-9565/ada9c5
Jorge J Martínez de Lejarza, David F Rentería-Estrada, Michele Grossi and Germán Rodrigo
We present the first quantum computation of a total decay rate in high-energy physics at second order in perturbative quantum field theory. This work underscores the confluence of two recent cutting-edge advances. On the one hand, the quantum integration algorithm quantum Fourier iterative amplitude estimation, which efficiently decomposes the target function into its Fourier series through a quantum neural network before quantumly integrating the corresponding Fourier components. On the other hand, causal unitary in the loop-tree duality (LTD), which exploits the causal properties of vacuum amplitudes in LTD to coherently generate all contributions with different numbers of final-state particles to a scattering or decay process, leading to singularity-free integrands that are well suited for Fourier decomposition. We test the performance of the quantum algorithm with benchmark decay rates in a quantum simulator and in quantum hardware, and find accurate theoretical predictions in both settings.
{"title":"Quantum integration of decay rates at second order in perturbation theory","authors":"Jorge J Martínez de Lejarza, David F Rentería-Estrada, Michele Grossi and Germán Rodrigo","doi":"10.1088/2058-9565/ada9c5","DOIUrl":"https://doi.org/10.1088/2058-9565/ada9c5","url":null,"abstract":"We present the first quantum computation of a total decay rate in high-energy physics at second order in perturbative quantum field theory. This work underscores the confluence of two recent cutting-edge advances. On the one hand, the quantum integration algorithm quantum Fourier iterative amplitude estimation, which efficiently decomposes the target function into its Fourier series through a quantum neural network before quantumly integrating the corresponding Fourier components. On the other hand, causal unitary in the loop-tree duality (LTD), which exploits the causal properties of vacuum amplitudes in LTD to coherently generate all contributions with different numbers of final-state particles to a scattering or decay process, leading to singularity-free integrands that are well suited for Fourier decomposition. We test the performance of the quantum algorithm with benchmark decay rates in a quantum simulator and in quantum hardware, and find accurate theoretical predictions in both settings.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"15 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2025-02-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143393570","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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