Pub Date : 2026-02-02DOI: 10.1088/2058-9565/ae3027
Soorya Rethinasamy, Ethan Guo, Alexander Wei, Mark M Wilde and Kristina D Launey
With a view toward addressing the explosive growth in the computational demands of nuclear structure and reactions modeling, we develop a novel quantum algorithm for neutron–nucleus simulations with general potentials, which provides acceptable bound-state energies even in the presence of noise, through the noise-resilient (NR) training method. In particular, the algorithm can now solve for any band-diagonal to full Hamiltonian matrices, as needed to accommodate a general central potential. While we illustrate the approach for exponential Gaussian-like potentials and ab initio inter-cluster potentials (optical potentials), it can also accommodate the complete form of the chiral effective-field-theory nucleon–nucleon potentials used in ab initio nuclear calculations. In this study, we provide a comprehensive analysis for the efficacy of this approach for three different qubit encodings, including the one-hot, binary, and Gray encodings, in terms of the number of Pauli strings and commuting sets involved. We also discuss the advantages of the algorithm for Hamiltonians of various band-diagonal widths, especially critical for potentials of perturbative nature, leading to a drastically reduced runtime of quantum simulations. We prove that the Gray encoding allows for an efficient scaling of the model-space size N (or number of basis states used) and is more resource efficient for band-diagonal Hamiltonians having bandwidth up to N. We introduce a new commutativity scheme called distance-grouped commutativity (DGC) and compare its performance with the well-known qubit-commutativity (QC) scheme. We lay out the explicit grouping of Pauli strings and the diagonalizing unitary under the DGC scheme, and we prove that it outperforms the QC scheme, at the cost of a more complex diagonalizing unitary. Lastly, we provide first solutions of the neutron–alpha dynamics from quantum simulations suitable for noisy intermediate-scale quantum processors, using an optical potential rooted in first principles, as well as a study of the bound-state physics in neutron–Carbon systems, along with a comparison of the efficacy of the one-hot and Gray encodings.
{"title":"Neutron–nucleus dynamics simulations for quantum computers","authors":"Soorya Rethinasamy, Ethan Guo, Alexander Wei, Mark M Wilde and Kristina D Launey","doi":"10.1088/2058-9565/ae3027","DOIUrl":"https://doi.org/10.1088/2058-9565/ae3027","url":null,"abstract":"With a view toward addressing the explosive growth in the computational demands of nuclear structure and reactions modeling, we develop a novel quantum algorithm for neutron–nucleus simulations with general potentials, which provides acceptable bound-state energies even in the presence of noise, through the noise-resilient (NR) training method. In particular, the algorithm can now solve for any band-diagonal to full Hamiltonian matrices, as needed to accommodate a general central potential. While we illustrate the approach for exponential Gaussian-like potentials and ab initio inter-cluster potentials (optical potentials), it can also accommodate the complete form of the chiral effective-field-theory nucleon–nucleon potentials used in ab initio nuclear calculations. In this study, we provide a comprehensive analysis for the efficacy of this approach for three different qubit encodings, including the one-hot, binary, and Gray encodings, in terms of the number of Pauli strings and commuting sets involved. We also discuss the advantages of the algorithm for Hamiltonians of various band-diagonal widths, especially critical for potentials of perturbative nature, leading to a drastically reduced runtime of quantum simulations. We prove that the Gray encoding allows for an efficient scaling of the model-space size N (or number of basis states used) and is more resource efficient for band-diagonal Hamiltonians having bandwidth up to N. We introduce a new commutativity scheme called distance-grouped commutativity (DGC) and compare its performance with the well-known qubit-commutativity (QC) scheme. We lay out the explicit grouping of Pauli strings and the diagonalizing unitary under the DGC scheme, and we prove that it outperforms the QC scheme, at the cost of a more complex diagonalizing unitary. Lastly, we provide first solutions of the neutron–alpha dynamics from quantum simulations suitable for noisy intermediate-scale quantum processors, using an optical potential rooted in first principles, as well as a study of the bound-state physics in neutron–Carbon systems, along with a comparison of the efficacy of the one-hot and Gray encodings.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"8 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146097945","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 : 2026-02-02DOI: 10.1088/2058-9565/ae397e
Dingjie Lu, Zhao Wang, Jun Liu, Yangfan Li, Wei-Bin Ewe and Zhuangjian Liu
This paper introduces a quantum-enhanced finite element method (FEM) designed for noisy intermediate-scale quantum (NISQ) devices, leveraging variational quantum algorithms (VQAs) to solve engineering partial differential equations. We demonstrate the framework by solving the Euler–Bernoulli beam and the NAFEMS T4 heat transfer problems, which involve Dirichlet, Neumann, and Robin boundary conditions. A key innovation is a ‘set-to-zero’ strategy that incorporates boundary conditions through a correction matrix, , allowing for flexible imposition at any node without domain decomposition. The global stiffness matrix is decomposed into a constant number of Pauli terms, O(1), using the method by Sato et al while boundary terms are handled with a sublinearly scaling partial Pauli measurement technique. The algorithm achieves logarithmic qubit scaling ( qubits for N degrees of freedom(DOF)) and employs shallow, hardware-efficient circuits with empirically trainable depth for small-scale systems. Validation on the Qiskit statevector simulator shows high accuracy. For the Euler–Bernoulli beam problem with 4 to 64 DOF, the algorithm achieves relative errors of 0.5%–1.5% and fidelities of 0.998–0.999. For the NAFEMS T4 heat transfer benchmark, a 5.4% relative error is observed. The VQA converges robustly within 77–350 iterations, though barren plateaus are a known challenge for scaling to larger systems. This work establishes a scalable framework for quantum FEM, offering a significant memory advantage over classical methods and advancing the potential for quantum-enhanced engineering simulations.
{"title":"Quantum finite element algorithm for solving Euler–Bernoulli and heat transfer PDEs with Dirichlet, Neumann, and Robin boundary conditions","authors":"Dingjie Lu, Zhao Wang, Jun Liu, Yangfan Li, Wei-Bin Ewe and Zhuangjian Liu","doi":"10.1088/2058-9565/ae397e","DOIUrl":"https://doi.org/10.1088/2058-9565/ae397e","url":null,"abstract":"This paper introduces a quantum-enhanced finite element method (FEM) designed for noisy intermediate-scale quantum (NISQ) devices, leveraging variational quantum algorithms (VQAs) to solve engineering partial differential equations. We demonstrate the framework by solving the Euler–Bernoulli beam and the NAFEMS T4 heat transfer problems, which involve Dirichlet, Neumann, and Robin boundary conditions. A key innovation is a ‘set-to-zero’ strategy that incorporates boundary conditions through a correction matrix, , allowing for flexible imposition at any node without domain decomposition. The global stiffness matrix is decomposed into a constant number of Pauli terms, O(1), using the method by Sato et al while boundary terms are handled with a sublinearly scaling partial Pauli measurement technique. The algorithm achieves logarithmic qubit scaling ( qubits for N degrees of freedom(DOF)) and employs shallow, hardware-efficient circuits with empirically trainable depth for small-scale systems. Validation on the Qiskit statevector simulator shows high accuracy. For the Euler–Bernoulli beam problem with 4 to 64 DOF, the algorithm achieves relative errors of 0.5%–1.5% and fidelities of 0.998–0.999. For the NAFEMS T4 heat transfer benchmark, a 5.4% relative error is observed. The VQA converges robustly within 77–350 iterations, though barren plateaus are a known challenge for scaling to larger systems. This work establishes a scalable framework for quantum FEM, offering a significant memory advantage over classical methods and advancing the potential for quantum-enhanced engineering simulations.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"42 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146097947","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 : 2026-01-30DOI: 10.1088/2058-9565/ae2202
Reyhaneh Aghaei Saem, Behrang Tafreshi, Zoë Holmes and Supanut Thanasilp
Identifying scalable circuit architectures remains a central challenge in variational quantum computing and quantum machine learning. Many approaches have been proposed to mitigate or avoid the barren plateau phenomenon or, more broadly, exponential concentration. However, due to the intricate interplay between quantum measurements and classical post-processing, we argue these techniques often fail to circumvent concentration effects in practice. Here, by analyzing concentration at the level of measurement outcome probabilities and leveraging tools from hypothesis testing, we develop a practical framework for diagnosing whether a parameterized quantum model is inhibited by exponential concentration. Applying this framework, we argue that several widely used methods (including quantum natural gradient, sample-based optimization, and certain neural-network-inspired initializations) do not overcome exponential concentration with finite measurement budgets, though they may still aid training in other ways.
{"title":"Pitfalls when tackling the exponential concentration of parameterized quantum models","authors":"Reyhaneh Aghaei Saem, Behrang Tafreshi, Zoë Holmes and Supanut Thanasilp","doi":"10.1088/2058-9565/ae2202","DOIUrl":"https://doi.org/10.1088/2058-9565/ae2202","url":null,"abstract":"Identifying scalable circuit architectures remains a central challenge in variational quantum computing and quantum machine learning. Many approaches have been proposed to mitigate or avoid the barren plateau phenomenon or, more broadly, exponential concentration. However, due to the intricate interplay between quantum measurements and classical post-processing, we argue these techniques often fail to circumvent concentration effects in practice. Here, by analyzing concentration at the level of measurement outcome probabilities and leveraging tools from hypothesis testing, we develop a practical framework for diagnosing whether a parameterized quantum model is inhibited by exponential concentration. Applying this framework, we argue that several widely used methods (including quantum natural gradient, sample-based optimization, and certain neural-network-inspired initializations) do not overcome exponential concentration with finite measurement budgets, though they may still aid training in other ways.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"44 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146072386","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 : 2026-01-29DOI: 10.1088/2058-9565/ae1e27
Steve Campbell, Irene D’Amico, Mario A Ciampini, Janet Anders, Natalia Ares, Simone Artini, Alexia Auffèves, Lindsay Bassman Oftelie, Laetitia P Bettmann, Marcus V S Bonança, Thomas Busch, Michele Campisi, Moallison F Cavalcante, Luis A Correa, Eloisa Cuestas, Ceren B Dag, Salambô Dago, Sebastian Deffner, Adolfo Del Campo, Andreas Deutschmann-Olek, Sandro Donadi, Emery Doucet, Cyril Elouard, Klaus Ensslin, Paul Erker, Nicole Fabbri, Federico Fedele, Guilherme Fiusa, Thomás Fogarty, Joshua Folk, Giacomo Guarnieri, Abhaya S Hegde, Santiago Hernández-Gómez, Chang-Kang Hu, Fernando Iemini, Bayan Karimi, Nikolai Kiesel, Gabriel T Landi, Aleksander Lasek, Sergei Lemziakov, Gabriele Lo Monaco, Eric Lutz, Dmitrii Lvov, Olivier Maillet, Mohammad Mehboudi, Taysa M Mendonça, Harry J D Miller, Andrew K Mitchell, Mark T Mitchison, Victor Mukherjee, Mauro Paternostro, Jukka Pekola, Martí Perarnau-Llobet, Ulrich Poschinger, Alberto Rolandi, Dario Rosa, Rafael Sánchez, Alan C Santos, Roberto..
The last two decades have seen quantum thermodynamics become a well established field of research in its own right. In that time, it has demonstrated a remarkably broad applicability, ranging from providing foundational advances in the understanding of how thermodynamic principles apply at the nano-scale and in the presence of quantum coherence, to providing a guiding framework for the development of efficient quantum devices. Exquisite levels of control have allowed state-of-the-art experimental platforms to explore energetics and thermodynamics at the smallest scales which has in turn helped to drive theoretical advances. This Roadmap provides an overview of the recent developments across many of the field’s sub-disciplines, assessing the key challenges and future prospects, providing a guide for its near term progress.
{"title":"Roadmap on quantum thermodynamics","authors":"Steve Campbell, Irene D’Amico, Mario A Ciampini, Janet Anders, Natalia Ares, Simone Artini, Alexia Auffèves, Lindsay Bassman Oftelie, Laetitia P Bettmann, Marcus V S Bonança, Thomas Busch, Michele Campisi, Moallison F Cavalcante, Luis A Correa, Eloisa Cuestas, Ceren B Dag, Salambô Dago, Sebastian Deffner, Adolfo Del Campo, Andreas Deutschmann-Olek, Sandro Donadi, Emery Doucet, Cyril Elouard, Klaus Ensslin, Paul Erker, Nicole Fabbri, Federico Fedele, Guilherme Fiusa, Thomás Fogarty, Joshua Folk, Giacomo Guarnieri, Abhaya S Hegde, Santiago Hernández-Gómez, Chang-Kang Hu, Fernando Iemini, Bayan Karimi, Nikolai Kiesel, Gabriel T Landi, Aleksander Lasek, Sergei Lemziakov, Gabriele Lo Monaco, Eric Lutz, Dmitrii Lvov, Olivier Maillet, Mohammad Mehboudi, Taysa M Mendonça, Harry J D Miller, Andrew K Mitchell, Mark T Mitchison, Victor Mukherjee, Mauro Paternostro, Jukka Pekola, Martí Perarnau-Llobet, Ulrich Poschinger, Alberto Rolandi, Dario Rosa, Rafael Sánchez, Alan C Santos, Roberto..","doi":"10.1088/2058-9565/ae1e27","DOIUrl":"https://doi.org/10.1088/2058-9565/ae1e27","url":null,"abstract":"The last two decades have seen quantum thermodynamics become a well established field of research in its own right. In that time, it has demonstrated a remarkably broad applicability, ranging from providing foundational advances in the understanding of how thermodynamic principles apply at the nano-scale and in the presence of quantum coherence, to providing a guiding framework for the development of efficient quantum devices. Exquisite levels of control have allowed state-of-the-art experimental platforms to explore energetics and thermodynamics at the smallest scales which has in turn helped to drive theoretical advances. This Roadmap provides an overview of the recent developments across many of the field’s sub-disciplines, assessing the key challenges and future prospects, providing a guide for its near term progress.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"33 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146070420","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 : 2026-01-29DOI: 10.1088/2058-9565/ae36cc
Jonathan Nemirovsky, Maya Chuchem and Yotam Shapira
As quantum processors grow in scale and reliability, the need for efficient quantum gate decomposition of circuits to a set of specific available gates, becomes ever more critical. The decomposition of a particular algorithm into a sequence of these available gates is not unique. Thus, the fidelity of an algorithm’s implementation can be increased by choosing an optimized decomposition. This is true both for noisy intermediate-scale quantum platforms as well as for implementation of quantum error correction schemes. Here we present a compilation scheme which implements a general-circuit decomposition to a sequence of Ising-type, long-range, multi-qubit (MQ) entangling gates, that are separated by layers of single qubit rotations. We use trapped ions as an example in which MQ gates naturally arise, yet any system that has connectivity beyond nearest-neighbors may gain from our approach. We evaluate our methods using the quantum volume (QV) test over N qubits. In this context, our method replaces two-qubit gates with MQ gates. Furthermore, our method minimizes the magnitude of the entanglement phases, which typically enables an improved implementation fidelity, by using weaker driving fields or faster realizations. We numerically test our compilation and show that, compared to conventional realizations with sequential two-qubit gates, our compilations improves the logarithm of QV by 20% to 25%.
{"title":"Efficient compilation of quantum circuits using multi-qubit gates","authors":"Jonathan Nemirovsky, Maya Chuchem and Yotam Shapira","doi":"10.1088/2058-9565/ae36cc","DOIUrl":"https://doi.org/10.1088/2058-9565/ae36cc","url":null,"abstract":"As quantum processors grow in scale and reliability, the need for efficient quantum gate decomposition of circuits to a set of specific available gates, becomes ever more critical. The decomposition of a particular algorithm into a sequence of these available gates is not unique. Thus, the fidelity of an algorithm’s implementation can be increased by choosing an optimized decomposition. This is true both for noisy intermediate-scale quantum platforms as well as for implementation of quantum error correction schemes. Here we present a compilation scheme which implements a general-circuit decomposition to a sequence of Ising-type, long-range, multi-qubit (MQ) entangling gates, that are separated by layers of single qubit rotations. We use trapped ions as an example in which MQ gates naturally arise, yet any system that has connectivity beyond nearest-neighbors may gain from our approach. We evaluate our methods using the quantum volume (QV) test over N qubits. In this context, our method replaces two-qubit gates with MQ gates. Furthermore, our method minimizes the magnitude of the entanglement phases, which typically enables an improved implementation fidelity, by using weaker driving fields or faster realizations. We numerically test our compilation and show that, compared to conventional realizations with sequential two-qubit gates, our compilations improves the logarithm of QV by 20% to 25%.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"117 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146070421","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 : 2026-01-28DOI: 10.1088/2058-9565/ae379e
Wei-Bin Chen, Ding Fang, Cheng-Hao Zhang, Jin-Ming Cui, Yun-Feng Huang, Chuan-Feng Li and Guang-Can Guo
Trapped ions in micro-cavities constitute a key platform for advancing quantum information processing and quantum networking. By providing an efficient light–matter interface within a compact architecture, they serve as highly efficient quantum nodes with strong potential for a scalable quantum network. However, in such systems, ion trapping stability is often compromised by surface charging effects, and nearby dielectric materials are known to cause a dramatic increase in the ion heating rate by several orders of magnitude. These challenges significantly hinder the practical implementation of ion trap systems integrated with micro-cavities. To overcome these limitations, we present the design and fabrication of metal-shielded fiber-cavity mirrors, enabling the stable realization of ion trap systems integrated with fiber cavities. Using this method, we constructed a needle ion trap integrated with a fiber Fabry–Pérot cavity and successfully achieved stable trapping of a single ion within the cavity. The measured ion heating rate was reduced by more than an order of magnitude compared with unshielded configurations. This work establishes a key technique toward fully integrated ion–photon interfaces for scalable quantum networks.
{"title":"Design and fabrication of metal-shielded fiber-cavity mirrors for ion-trap systems","authors":"Wei-Bin Chen, Ding Fang, Cheng-Hao Zhang, Jin-Ming Cui, Yun-Feng Huang, Chuan-Feng Li and Guang-Can Guo","doi":"10.1088/2058-9565/ae379e","DOIUrl":"https://doi.org/10.1088/2058-9565/ae379e","url":null,"abstract":"Trapped ions in micro-cavities constitute a key platform for advancing quantum information processing and quantum networking. By providing an efficient light–matter interface within a compact architecture, they serve as highly efficient quantum nodes with strong potential for a scalable quantum network. However, in such systems, ion trapping stability is often compromised by surface charging effects, and nearby dielectric materials are known to cause a dramatic increase in the ion heating rate by several orders of magnitude. These challenges significantly hinder the practical implementation of ion trap systems integrated with micro-cavities. To overcome these limitations, we present the design and fabrication of metal-shielded fiber-cavity mirrors, enabling the stable realization of ion trap systems integrated with fiber cavities. Using this method, we constructed a needle ion trap integrated with a fiber Fabry–Pérot cavity and successfully achieved stable trapping of a single ion within the cavity. The measured ion heating rate was reduced by more than an order of magnitude compared with unshielded configurations. This work establishes a key technique toward fully integrated ion–photon interfaces for scalable quantum networks.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"42 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146056981","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 : 2026-01-28DOI: 10.1088/2058-9565/ae34e1
Yan Lu and Xiao-Feng Shi
Large-scale Greenberger–Horne–Zeilinger (GHZ) state is useful for quantum technologies but difficult to be prepared. Here, we propose fast measurement-based preparation of large-scale GHZ states by a four-qubit quantum phase gate with nuclear-spin qubits of alkaline-earth-like atoms, which is named as quantum ferromagnetic gate due to its analogy to the alignment of molecular magnetic moments in a classical magnet. A high-fidelity Rydberg-mediated QFG can be realized in a time of with the maximal Rydberg Rabi frequency. From a product state of three data atoms and one ancilla atom, a gluing circuit with one QFG, two single-qubit gates, and a projective measurement of the ancilla can generate a 3-qubit GHZ state, and repetition of this gluing circuit can lead to 9, 27, 81, 243 -qubit GHZ states. Analyses based on currently available techniques show that a 243-qubit GHZ state is realizable, and more qubits can be entangled with higher detection fidelity.
{"title":"Fast measurement-based generation of large-scale Greenberger–Horne–Zeilinger state with atomic nuclear-spin qubits","authors":"Yan Lu and Xiao-Feng Shi","doi":"10.1088/2058-9565/ae34e1","DOIUrl":"https://doi.org/10.1088/2058-9565/ae34e1","url":null,"abstract":"Large-scale Greenberger–Horne–Zeilinger (GHZ) state is useful for quantum technologies but difficult to be prepared. Here, we propose fast measurement-based preparation of large-scale GHZ states by a four-qubit quantum phase gate with nuclear-spin qubits of alkaline-earth-like atoms, which is named as quantum ferromagnetic gate due to its analogy to the alignment of molecular magnetic moments in a classical magnet. A high-fidelity Rydberg-mediated QFG can be realized in a time of with the maximal Rydberg Rabi frequency. From a product state of three data atoms and one ancilla atom, a gluing circuit with one QFG, two single-qubit gates, and a projective measurement of the ancilla can generate a 3-qubit GHZ state, and repetition of this gluing circuit can lead to 9, 27, 81, 243 -qubit GHZ states. Analyses based on currently available techniques show that a 243-qubit GHZ state is realizable, and more qubits can be entangled with higher detection fidelity.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"15 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146056980","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 : 2026-01-28DOI: 10.1088/2058-9565/ae379d
Hiroyoshi Kurogi, Katsuhiro Endo, Yuki Sato, Michihiko Sugawara, Kaito Wada, Kenji Sugisaki, Shu Kanno, Hiroshi C Watanabe and Haruyuki Nakano
In variational quantum algorithms (VQAs), parameterization is typically applied to single-qubit gates. In this study, we instead parameterize a generalized controlled gate and propose an algorithm to locally minimize the cost function by maximally optimizing these parameters. This method extends the free quaternion selection technique, which was originally developed for single-qubit gate optimization. To evaluate its performance, we apply the proposed method to a variety of quantum optimization tasks, including the variational quantum eigensolver for both Ising and molecular Hamiltonians, fidelity maximization in general VQAs, and unitary compilation of time evolution operators. Across these applications, our method demonstrates efficient optimization, enhanced expressibility, and the ability to construct shallower circuits compared to existing techniques. Moreover, the method can be generalized to optimize particle-number-conserving gates, which are particularly relevant for quantum chemistry. Leveraging this capability, we further demonstrate that the method achieves superior quantum compilation of molecular time-evolution operators by approximating them with shallower circuits than standard Trotter decomposition.
{"title":"Optimizing a parameterized controlled gate using free quaternion selection","authors":"Hiroyoshi Kurogi, Katsuhiro Endo, Yuki Sato, Michihiko Sugawara, Kaito Wada, Kenji Sugisaki, Shu Kanno, Hiroshi C Watanabe and Haruyuki Nakano","doi":"10.1088/2058-9565/ae379d","DOIUrl":"https://doi.org/10.1088/2058-9565/ae379d","url":null,"abstract":"In variational quantum algorithms (VQAs), parameterization is typically applied to single-qubit gates. In this study, we instead parameterize a generalized controlled gate and propose an algorithm to locally minimize the cost function by maximally optimizing these parameters. This method extends the free quaternion selection technique, which was originally developed for single-qubit gate optimization. To evaluate its performance, we apply the proposed method to a variety of quantum optimization tasks, including the variational quantum eigensolver for both Ising and molecular Hamiltonians, fidelity maximization in general VQAs, and unitary compilation of time evolution operators. Across these applications, our method demonstrates efficient optimization, enhanced expressibility, and the ability to construct shallower circuits compared to existing techniques. Moreover, the method can be generalized to optimize particle-number-conserving gates, which are particularly relevant for quantum chemistry. Leveraging this capability, we further demonstrate that the method achieves superior quantum compilation of molecular time-evolution operators by approximating them with shallower circuits than standard Trotter decomposition.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"295 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146056984","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 : 2026-01-28DOI: 10.1088/2058-9565/ae390d
Dávid Szász-Schagrin, Daniele Cristani, Lorenzo Piroli and Eric Vernier
We provide a systematic construction for local quantum circuits hosting free fermions in disguise (FFD), both with staircase and brickwork architectures. Similar to the original Hamiltonian model introduced by Fendley, these circuits are defined by the fact that the Floquet operator corresponding to a single time step can not be diagonalized by means of any Jordan–Wigner transformation, but still displays a free-fermionic spectrum. Our construction makes use of suitable non-local transfer matrices commuting with the Floquet operator, allowing us to establish the free fermionic spectrum. We also study the dynamics of these circuits after they are initialized in arbitrary product states, proving that the evolution of certain local observables can be simulated efficiently on classical computers. Our work proves recent conjectures in the literature and raises new questions on the classical simulability of FFD.
{"title":"Construction and simulability of quantum circuits with free fermions in disguise","authors":"Dávid Szász-Schagrin, Daniele Cristani, Lorenzo Piroli and Eric Vernier","doi":"10.1088/2058-9565/ae390d","DOIUrl":"https://doi.org/10.1088/2058-9565/ae390d","url":null,"abstract":"We provide a systematic construction for local quantum circuits hosting free fermions in disguise (FFD), both with staircase and brickwork architectures. Similar to the original Hamiltonian model introduced by Fendley, these circuits are defined by the fact that the Floquet operator corresponding to a single time step can not be diagonalized by means of any Jordan–Wigner transformation, but still displays a free-fermionic spectrum. Our construction makes use of suitable non-local transfer matrices commuting with the Floquet operator, allowing us to establish the free fermionic spectrum. We also study the dynamics of these circuits after they are initialized in arbitrary product states, proving that the evolution of certain local observables can be simulated efficiently on classical computers. Our work proves recent conjectures in the literature and raises new questions on the classical simulability of FFD.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"73 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146056986","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 : 2026-01-28DOI: 10.1088/2058-9565/ae34e3
Mitchell J Walker, Ryuji Moriya, Jack D Segal, Liam A P Gallagher, Matthew Hill, Frédéric Leroux, Zhongxiao Xu and Matthew P A Jones
Arrays of neutral atoms in optical tweezers are widely used in quantum simulation and computation, and precision frequency metrology. The capabilities of these arrays are enhanced by maximising the number of available sites. Here we increase the spatial extent of a two-dimensional array of 88Sr atoms by sweeping the frequency of the cooling light to move the atomic reservoir across the array. We load arrays with vertical heights of 100 µm, exceeding the height of an array loaded from a static reservoir by a factor of 3. We investigate the site-to-site atom number distribution, tweezer lifetime, and temperature, achieving an average temperature across the array of µK. By controlling the frequency sweep we show it is possible to control the distribution of atoms across the array, including uniform and non-uniformly loaded arrays, and arrays with selectively loaded regions. We explain our results using a rate equation model which is in qualitative agreement with the data.
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