Pub Date : 2026-01-16DOI: 10.1088/2058-9565/ae3029
Alejandro Villoria, Henning Basold and Alfons Laarman
Compiling quantum circuits to account for hardware restrictions is an essential part of the quantum computing stack. Circuit compilation allows us to adapt algorithm descriptions into a sequence of operations supported by real quantum hardware, and has the potential to significantly improve their performance when optimisation techniques are added to the process. One such optimisation technique is reducing the number of quantum gates that are needed to execute a circuit. For instance, methods for reducing the number of non-Clifford gates or CNOT gates from a circuit are an extensive research area that has gathered significant interest over the years. For certain hardware platforms such as trapped-ion quantum computers, we can leverage some of their special properties to further reduce the cost of executing a quantum circuit in them. In this work we use global interactions, such as the Global Mølmer–Sørensen (MS) gate present in trapped-ion hardware, to optimise and synthesise quantum circuits. We design and implement an algorithm that is able to compile an arbitrary quantum circuit into another circuit that uses global gates as the entangling operation, while optimising the number of global interactions needed. The algorithm is based on the ZX-calculus and uses a specialised circuit extraction routine that groups entangling gates into Global MS gates. We benchmark the algorithm in a variety of circuits, and show how it improves their performance under state-of-the-art hardware considerations in comparison to a naive algorithm and the Qiskit optimiser.
{"title":"Optimisation and synthesis of quantum circuits with global gates","authors":"Alejandro Villoria, Henning Basold and Alfons Laarman","doi":"10.1088/2058-9565/ae3029","DOIUrl":"https://doi.org/10.1088/2058-9565/ae3029","url":null,"abstract":"Compiling quantum circuits to account for hardware restrictions is an essential part of the quantum computing stack. Circuit compilation allows us to adapt algorithm descriptions into a sequence of operations supported by real quantum hardware, and has the potential to significantly improve their performance when optimisation techniques are added to the process. One such optimisation technique is reducing the number of quantum gates that are needed to execute a circuit. For instance, methods for reducing the number of non-Clifford gates or CNOT gates from a circuit are an extensive research area that has gathered significant interest over the years. For certain hardware platforms such as trapped-ion quantum computers, we can leverage some of their special properties to further reduce the cost of executing a quantum circuit in them. In this work we use global interactions, such as the Global Mølmer–Sørensen (MS) gate present in trapped-ion hardware, to optimise and synthesise quantum circuits. We design and implement an algorithm that is able to compile an arbitrary quantum circuit into another circuit that uses global gates as the entangling operation, while optimising the number of global interactions needed. The algorithm is based on the ZX-calculus and uses a specialised circuit extraction routine that groups entangling gates into Global MS gates. We benchmark the algorithm in a variety of circuits, and show how it improves their performance under state-of-the-art hardware considerations in comparison to a naive algorithm and the Qiskit optimiser.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"41 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145972324","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 : 2026-01-16DOI: 10.1088/2058-9565/ae30a2
Ji-Qian Qin, Yunlong Yu and Xiang-Bin Wang
Quantum annealing (QA) offers a promising approach for solving constrained combinatorial optimization on near-term quantum devices. It encodes solutions into the ground states of the Ising problem Hamiltonians through penalty terms and penalty parameters to enforce constraints. We propose a variational determination framework to address the issue of penalty parameter selection through three progressively generalized methods: the Frozen method variationally adjusts parameters in a tunable Hamiltonian to prepare evolved states minimizing the energy of a target Hamiltonian with Frozen parameters; the Time-Transfer method applies optimized parameters to longer annealing times; and the Full-Transfer method extends this approach across both system sizes and annealing durations. The effectiveness of these methods stems from energy minimization steering the evolution toward the low-energy subspace. Evaluated on vertex cover problems over 40 randomly generated 12-vertex 3-regular graphs, the Frozen method improves the average single-run success probability from to at , and reduces the average number of runs required for 99.9% success probability by 3.8 times at (including optimization overhead). Crucially, both Time-Transfer method and Full-Transfer method achieve single-run fidelity improvements comparable to the Frozen method, while reducing the number of runs required for 99.9% success probability at by 6.63 times and 6.4 times, respectively. The speedup of the Time-Transfer method excludes initial optimization at , whereas Full-Transfer method provides end-to-end acceleration. Our variational framework establishes that optimization-informed short-time QA can match the performance of extended schedules, offering a practical approach for current quantum devices.
{"title":"Variational determination of penalty parameters in quantum annealing","authors":"Ji-Qian Qin, Yunlong Yu and Xiang-Bin Wang","doi":"10.1088/2058-9565/ae30a2","DOIUrl":"https://doi.org/10.1088/2058-9565/ae30a2","url":null,"abstract":"Quantum annealing (QA) offers a promising approach for solving constrained combinatorial optimization on near-term quantum devices. It encodes solutions into the ground states of the Ising problem Hamiltonians through penalty terms and penalty parameters to enforce constraints. We propose a variational determination framework to address the issue of penalty parameter selection through three progressively generalized methods: the Frozen method variationally adjusts parameters in a tunable Hamiltonian to prepare evolved states minimizing the energy of a target Hamiltonian with Frozen parameters; the Time-Transfer method applies optimized parameters to longer annealing times; and the Full-Transfer method extends this approach across both system sizes and annealing durations. The effectiveness of these methods stems from energy minimization steering the evolution toward the low-energy subspace. Evaluated on vertex cover problems over 40 randomly generated 12-vertex 3-regular graphs, the Frozen method improves the average single-run success probability from to at , and reduces the average number of runs required for 99.9% success probability by 3.8 times at (including optimization overhead). Crucially, both Time-Transfer method and Full-Transfer method achieve single-run fidelity improvements comparable to the Frozen method, while reducing the number of runs required for 99.9% success probability at by 6.63 times and 6.4 times, respectively. The speedup of the Time-Transfer method excludes initial optimization at , whereas Full-Transfer method provides end-to-end acceleration. Our variational framework establishes that optimization-informed short-time QA can match the performance of extended schedules, offering a practical approach for current quantum devices.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"60 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145972325","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 : 2026-01-13DOI: 10.1088/2058-9565/ae30a4
Mu-En Liu, Kai-Siang Chen, Chung-Yun Hsieh, Gelo Noel M Tabia and Yeong-Cherng Liang
Generic bipartite pure states of sufficiently large dimensions are overwhelmingly likely to be highly entangled. However, unlike the bipartite setting, the entanglement of generic multipartite pure states, and specifically their multipartite marginals, is far less understood. Here, we show that sufficiently large marginals of generic multipartite pure states, accounting for approximately half or more of the subsystems, are entangled across all bipartitions. These pure states are thus robust to losses in entanglement distribution. Moreover, even without assuming that the global state is pure, a small number of overlapping entangled marginals of generic pure states—as we show in this work—must induce entanglement in other marginals when some mild dimension constraints are satisfied, i.e. entanglement transitivity is a generic feature of various many-body pure states. Numerically, we further observe that the genericity of (1) entangled marginals, (2) unique global compatibility, and (3) entanglement transitivity may also hold beyond the analytically established dimension constraints. We also discuss potential applications of these features of generic pure states in quantum information processing.
{"title":"Large parts are generically entangled across all cuts","authors":"Mu-En Liu, Kai-Siang Chen, Chung-Yun Hsieh, Gelo Noel M Tabia and Yeong-Cherng Liang","doi":"10.1088/2058-9565/ae30a4","DOIUrl":"https://doi.org/10.1088/2058-9565/ae30a4","url":null,"abstract":"Generic bipartite pure states of sufficiently large dimensions are overwhelmingly likely to be highly entangled. However, unlike the bipartite setting, the entanglement of generic multipartite pure states, and specifically their multipartite marginals, is far less understood. Here, we show that sufficiently large marginals of generic multipartite pure states, accounting for approximately half or more of the subsystems, are entangled across all bipartitions. These pure states are thus robust to losses in entanglement distribution. Moreover, even without assuming that the global state is pure, a small number of overlapping entangled marginals of generic pure states—as we show in this work—must induce entanglement in other marginals when some mild dimension constraints are satisfied, i.e. entanglement transitivity is a generic feature of various many-body pure states. Numerically, we further observe that the genericity of (1) entangled marginals, (2) unique global compatibility, and (3) entanglement transitivity may also hold beyond the analytically established dimension constraints. We also discuss potential applications of these features of generic pure states in quantum information processing.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"46 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145955104","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 : 2026-01-12DOI: 10.1088/2058-9565/ae30a3
Jiheon Seong, Anindita Bera, Beatrix C Hiesmayr, Dariusz Chruściński and Joonwoo Bae
Entanglement witnesses (EWs) are a versatile tool to detect entangled states and characterize related properties of entanglement in quantum information theory. The verification of entangled states via EWs relies on the fact that separable states form a convex set; this also means that the framework presented by EWs generally applies to other quantum resources where free resources contain the convexity. A witness W corresponds to an observable satisfying for all separable states ; entangled states are detected once the inequality is violated. Recently, mirrored EWs have been introduced by showing that there exist non-trivial upper bounds to EWs, An upper bound to a witness W signifies the existence of the other one M, called a mirrored EW, such that . The framework of mirrored EWs shows that a single EW can be even more useful, as it can detect a larger set of entangled states by lower and upper bounds. In this work, we develop and investigate mirrored EWs for multipartite qubit states and also for high-dimensional systems, to find the efficiency and effectiveness of mirrored EWs in detecting entangled states. We provide mirrored EWs for n-partite GHZ states, graph states such as two-colorable states and tripartite bound entangled states. We also show that optimal EWs can be reflected with each other. For bipartite systems, we present mirrored EWs for existing optimal EWs and also construct a mirrored pair of optimal EWs in dimension three. Finally, we generalize mirrored EWs such that a pair of EWs can be connected by another EW, i.e. is also an EW. Our results enhance the capability of EWs to detect a larger set of entangled states in multipartite and high-dimensional quantum systems.
{"title":"Mirrored entanglement witnesses for multipartite and high-dimensional quantum systems","authors":"Jiheon Seong, Anindita Bera, Beatrix C Hiesmayr, Dariusz Chruściński and Joonwoo Bae","doi":"10.1088/2058-9565/ae30a3","DOIUrl":"https://doi.org/10.1088/2058-9565/ae30a3","url":null,"abstract":"Entanglement witnesses (EWs) are a versatile tool to detect entangled states and characterize related properties of entanglement in quantum information theory. The verification of entangled states via EWs relies on the fact that separable states form a convex set; this also means that the framework presented by EWs generally applies to other quantum resources where free resources contain the convexity. A witness W corresponds to an observable satisfying for all separable states ; entangled states are detected once the inequality is violated. Recently, mirrored EWs have been introduced by showing that there exist non-trivial upper bounds to EWs, An upper bound to a witness W signifies the existence of the other one M, called a mirrored EW, such that . The framework of mirrored EWs shows that a single EW can be even more useful, as it can detect a larger set of entangled states by lower and upper bounds. In this work, we develop and investigate mirrored EWs for multipartite qubit states and also for high-dimensional systems, to find the efficiency and effectiveness of mirrored EWs in detecting entangled states. We provide mirrored EWs for n-partite GHZ states, graph states such as two-colorable states and tripartite bound entangled states. We also show that optimal EWs can be reflected with each other. For bipartite systems, we present mirrored EWs for existing optimal EWs and also construct a mirrored pair of optimal EWs in dimension three. Finally, we generalize mirrored EWs such that a pair of EWs can be connected by another EW, i.e. is also an EW. Our results enhance the capability of EWs to detect a larger set of entangled states in multipartite and high-dimensional quantum systems.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"191 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145950005","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 : 2026-01-07DOI: 10.1088/2058-9565/ae3028
Qiaofeng Liu, Ian Low and Zhewei Yin
Magic is a quantum resource essential for universal quantum computation and represents the deviation of quantum states from those that can be simulated efficiently using classical algorithms. Using the stabilizer Rényi entropy (SRE), we investigate two-qubit states with maximal magic, which are most distinct from classical simulability, and provide strong numerical evidence that the maximal second order SRE is , establishing a tighter bound than the prior . We identify 480 states saturating the new bound, which turn out to be the fiducial states for the mutually unbiased bases (MUBs) generated by the orbits of the Weyl–Heisenberg (WH) group, and conjecture that WH-MUBs are the maximal magic states for n-qubit, when n ≠ 1 and 3. We also reveal a striking interplay between magic and entanglement: the entanglement of maximal magic states is restricted to two possible values, and , as quantified by the concurrence; none is maximally entangled.
{"title":"Maximal magic for two-qubit states","authors":"Qiaofeng Liu, Ian Low and Zhewei Yin","doi":"10.1088/2058-9565/ae3028","DOIUrl":"https://doi.org/10.1088/2058-9565/ae3028","url":null,"abstract":"Magic is a quantum resource essential for universal quantum computation and represents the deviation of quantum states from those that can be simulated efficiently using classical algorithms. Using the stabilizer Rényi entropy (SRE), we investigate two-qubit states with maximal magic, which are most distinct from classical simulability, and provide strong numerical evidence that the maximal second order SRE is , establishing a tighter bound than the prior . We identify 480 states saturating the new bound, which turn out to be the fiducial states for the mutually unbiased bases (MUBs) generated by the orbits of the Weyl–Heisenberg (WH) group, and conjecture that WH-MUBs are the maximal magic states for n-qubit, when n ≠ 1 and 3. We also reveal a striking interplay between magic and entanglement: the entanglement of maximal magic states is restricted to two possible values, and , as quantified by the concurrence; none is maximally entangled.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"40 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145908302","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 : 2026-01-06DOI: 10.1088/2058-9565/ae2efa
Dmitrii Khitrin, Kenneth R Brown and Abhinav Anand
Unitary errors, such as those arising from fault-tolerant (FT) compilation of quantum algorithms, systematically bias observable estimates. Correcting this bias typically requires additional resources, such as an increased number of non-Clifford gates. In this work, we present an alternative method for correcting bias in the expectation values of observables. The method leverages a decomposition of the ideal quantum channel into a probabilistic mixture of noisy quantum channels. Using this decomposition, we construct unbiased estimators as weighted sums of expectation values obtained from the noisy channels. We provide a detailed analysis of the method, identify the conditions under which it is effective, and validate its performance through numerical simulations. In particular, we demonstrate unbiased observable estimation in the presence of unitary errors by simulating the time dynamics of the Ising Hamiltonian. Our strategy offers a resource-efficient way to reduce the impact of unitary errors, improving methods for estimating observables in noisy near-term quantum devices and FT implementation of quantum algorithms.
{"title":"Unbiased observable estimation with approximate channels in fault-tolerant quantum computation","authors":"Dmitrii Khitrin, Kenneth R Brown and Abhinav Anand","doi":"10.1088/2058-9565/ae2efa","DOIUrl":"https://doi.org/10.1088/2058-9565/ae2efa","url":null,"abstract":"Unitary errors, such as those arising from fault-tolerant (FT) compilation of quantum algorithms, systematically bias observable estimates. Correcting this bias typically requires additional resources, such as an increased number of non-Clifford gates. In this work, we present an alternative method for correcting bias in the expectation values of observables. The method leverages a decomposition of the ideal quantum channel into a probabilistic mixture of noisy quantum channels. Using this decomposition, we construct unbiased estimators as weighted sums of expectation values obtained from the noisy channels. We provide a detailed analysis of the method, identify the conditions under which it is effective, and validate its performance through numerical simulations. In particular, we demonstrate unbiased observable estimation in the presence of unitary errors by simulating the time dynamics of the Ising Hamiltonian. Our strategy offers a resource-efficient way to reduce the impact of unitary errors, improving methods for estimating observables in noisy near-term quantum devices and FT implementation of quantum algorithms.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"1 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2026-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145902619","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 : 2025-12-31DOI: 10.1088/2058-9565/ae2d8d
Christopher Mastandrea, Costin Iancu, Hao Guo, Chih-Chun Chien
A spin-1 system can exhibit an intermediate-temperature topological regime with a quantized Uhlmann phase sandwiched by topologically trivial low- and high-temperature regimes. We present a quantum circuit consisting of system and ancilla qubits plus a probe qubit which prepares an initial state corresponding to the purified state of a spin-1 system at finite temperature, evolves the system according to the Uhlmann process, and measures the Uhlmann phase via expectation values of the probe qubit. Although classical simulations suggest the quantized Uhlmann phase is observable on International Business Machines (IBM’s) noisy intermediate-scale quantum (NISQ) computers, an implementation of the circuit without any optimization exceeds the gate count for the error budget and results in unresolved signals. Through a series of optimization with Qiskit and BQSKit, the gate count can be substantially reduced, making the jumps of the Uhlmann phase more visible. A recent hardware upgrade of IBM quantum computers further improves the signals and leads to a clearer demonstration of interesting finite-temperature topological phenomena on NISQ hardware.
{"title":"Intermediate-temperature topological Uhlmann phase on IBM quantum computers","authors":"Christopher Mastandrea, Costin Iancu, Hao Guo, Chih-Chun Chien","doi":"10.1088/2058-9565/ae2d8d","DOIUrl":"https://doi.org/10.1088/2058-9565/ae2d8d","url":null,"abstract":"A spin-1 system can exhibit an intermediate-temperature topological regime with a quantized Uhlmann phase sandwiched by topologically trivial low- and high-temperature regimes. We present a quantum circuit consisting of system and ancilla qubits plus a probe qubit which prepares an initial state corresponding to the purified state of a spin-1 system at finite temperature, evolves the system according to the Uhlmann process, and measures the Uhlmann phase via expectation values of the probe qubit. Although classical simulations suggest the quantized Uhlmann phase is observable on International Business Machines (IBM’s) noisy intermediate-scale quantum (NISQ) computers, an implementation of the circuit without any optimization exceeds the gate count for the error budget and results in unresolved signals. Through a series of optimization with Qiskit and BQSKit, the gate count can be substantially reduced, making the jumps of the Uhlmann phase more visible. A recent hardware upgrade of IBM quantum computers further improves the signals and leads to a clearer demonstration of interesting finite-temperature topological phenomena on NISQ hardware.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"24 1","pages":"015033"},"PeriodicalIF":6.7,"publicationDate":"2025-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894229","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 : 2025-12-31DOI: 10.1088/2058-9565/ae302a
Xuan Zuo, Zi-Xu Lu, Jie Li
The strong coupling between light and matter gives rise to polaritons. Further coupling polaritons to phonons leads to the formation of hybrid polaromechanical systems. Recent experiments have achieved the strong coupling between polaritons and phonons in two configurations, namely, the magnon–photon–phonon and exciton–photon–phonon systems, which enables the control of mechanical motion via manipulating polaritons. Here, we present a polaromechanical cooling theory and explicitly show how two polaritons can be used to simultaneously cool two mechanical modes. The unique advantage of our protocol lies in the fact that the continuous tunability of the polariton frequencies over a wide range allows for the cooling of any two mechanical modes with their frequency difference falling within this range. We further discuss how to extend the theory to cool multiple mechanical modes. The protocol is designed for cooling mechanical motion in various emerging polaromechanical platforms, such as magnon-, exciton-, and plasmon-polaromechanical systems, which is the first step towards quantum states generation in these hybrid systems.
{"title":"Cooling mechanical motion with polaritons","authors":"Xuan Zuo, Zi-Xu Lu, Jie Li","doi":"10.1088/2058-9565/ae302a","DOIUrl":"https://doi.org/10.1088/2058-9565/ae302a","url":null,"abstract":"The strong coupling between light and matter gives rise to polaritons. Further coupling polaritons to phonons leads to the formation of hybrid polaromechanical systems. Recent experiments have achieved the strong coupling between polaritons and phonons in two configurations, namely, the magnon–photon–phonon and exciton–photon–phonon systems, which enables the control of mechanical motion via manipulating polaritons. Here, we present a polaromechanical cooling theory and explicitly show how two polaritons can be used to simultaneously cool two mechanical modes. The unique advantage of our protocol lies in the fact that the continuous tunability of the polariton frequencies over a wide range allows for the cooling of any two mechanical modes with their frequency difference falling within this range. We further discuss how to extend the theory to cool multiple mechanical modes. The protocol is designed for cooling mechanical motion in various emerging polaromechanical platforms, such as magnon-, exciton-, and plasmon-polaromechanical systems, which is the first step towards quantum states generation in these hybrid systems.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"25 1","pages":"015032"},"PeriodicalIF":6.7,"publicationDate":"2025-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894231","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 : 2025-12-29DOI: 10.1088/2058-9565/ae2d8e
Asghar Ullah, Özgür E Müstecaplıoğlu, Matteo G A Paris
We investigate the optimization of graph topologies for quantum sensing networks designed to estimate weak magnetic fields. The sensors are modeled as spin systems governed by a transverse-field Ising Hamiltonian in thermal equilibrium at low temperatures. Using a genetic algorithm (GA), we evolve network topologies to maximize a perturbative spectral sensitivity measure, which serves as the fitness function for the GA. For the best-performing graphs, we compute the corresponding quantum Fisher information (QFI) to assess the ultimate bounds on estimation precision. To enable efficient scaling, we use the GA-generated data to train a deep neural network, allowing extrapolation to larger graph sizes where direct computation becomes prohibitive. Our results show that while both the fitness function and QFI initially increase with system size, the QFI exhibits a clear non-monotonic behavior—saturating and eventually declining beyond a critical graph size. This reflects the loss of superlinear scaling of the QFI, as the narrowing of the energy gap signals a crossover to classical scaling of the QFI with system size. The effect is reminiscent of the microeconomic law of diminishing returns: beyond an optimal graph size, further increases yield reduced sensing performance. This saturation and decline in precision are particularly pronounced under Kac scaling, where both the QFI and spin squeezing plateau or degrade with increasing system size. We also attribute observed even–odd oscillations in the spectral sensitivity measure and QFI to quantum interference effects in spin phase space, as confirmed by our phase-space analysis. These findings highlight the critical role of optimizing interaction topology—rather than simply increasing network size—and demonstrate the potential of hybrid evolutionary and learning-based approaches for designing high-performance quantum sensors.
{"title":"Optimizing quantum sensing networks via genetic algorithms and deep learning","authors":"Asghar Ullah, Özgür E Müstecaplıoğlu, Matteo G A Paris","doi":"10.1088/2058-9565/ae2d8e","DOIUrl":"https://doi.org/10.1088/2058-9565/ae2d8e","url":null,"abstract":"We investigate the optimization of graph topologies for quantum sensing networks designed to estimate weak magnetic fields. The sensors are modeled as spin systems governed by a transverse-field Ising Hamiltonian in thermal equilibrium at low temperatures. Using a genetic algorithm (GA), we evolve network topologies to maximize a perturbative spectral sensitivity measure, which serves as the fitness function for the GA. For the best-performing graphs, we compute the corresponding quantum Fisher information (QFI) to assess the ultimate bounds on estimation precision. To enable efficient scaling, we use the GA-generated data to train a deep neural network, allowing extrapolation to larger graph sizes where direct computation becomes prohibitive. Our results show that while both the fitness function and QFI initially increase with system size, the QFI exhibits a clear non-monotonic behavior—saturating and eventually declining beyond a critical graph size. This reflects the loss of superlinear scaling of the QFI, as the narrowing of the energy gap signals a crossover to classical scaling of the QFI with system size. The effect is reminiscent of the microeconomic law of diminishing returns: beyond an optimal graph size, further increases yield reduced sensing performance. This saturation and decline in precision are particularly pronounced under Kac scaling, where both the QFI and spin squeezing plateau or degrade with increasing system size. We also attribute observed even–odd oscillations in the spectral sensitivity measure and QFI to quantum interference effects in spin phase space, as confirmed by our phase-space analysis. These findings highlight the critical role of optimizing interaction topology—rather than simply increasing network size—and demonstrate the potential of hybrid evolutionary and learning-based approaches for designing high-performance quantum sensors.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"89 1","pages":"015031"},"PeriodicalIF":6.7,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894254","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 : 2025-12-23DOI: 10.1088/2058-9565/ae2c16
Leander Grech, Matthias G Krauss, Mirko Consiglio, Tony J G Apollaro, Christiane P Koch, Simon Hirlaender and Gianluca Valentino
Noisy intermediate-scale quantum computers hold the promise of tackling complex and otherwise intractable computational challenges through the massive parallelism offered by qubits. Central to realizing the potential of quantum computing are perfect entangling (PE) two-qubit gates, which serve as a critical building block for universal quantum computation. In the context of quantum optimal control, shaping electromagnetic pulses to drive quantum gates is crucial for pushing gate performance toward theoretical limits. In this work, we leverage reinforcement learning (RL) techniques to discover near-optimal pulse shapes that yield PE gates. A collection of RL agents is trained within robust simulation environments, enabling the identification of effective control strategies even under noisy conditions. Selected agents are then validated on higher-fidelity simulations, illustrating how RL-based methods can reduce calibration overhead when compared to quantum optimal control techniques. Furthermore, the RL approach is hardware agnostic with the potential for broad applicability across various quantum computing platforms.
{"title":"Achieving fast and robust perfect entangling gates via reinforcement learning","authors":"Leander Grech, Matthias G Krauss, Mirko Consiglio, Tony J G Apollaro, Christiane P Koch, Simon Hirlaender and Gianluca Valentino","doi":"10.1088/2058-9565/ae2c16","DOIUrl":"https://doi.org/10.1088/2058-9565/ae2c16","url":null,"abstract":"Noisy intermediate-scale quantum computers hold the promise of tackling complex and otherwise intractable computational challenges through the massive parallelism offered by qubits. Central to realizing the potential of quantum computing are perfect entangling (PE) two-qubit gates, which serve as a critical building block for universal quantum computation. In the context of quantum optimal control, shaping electromagnetic pulses to drive quantum gates is crucial for pushing gate performance toward theoretical limits. In this work, we leverage reinforcement learning (RL) techniques to discover near-optimal pulse shapes that yield PE gates. A collection of RL agents is trained within robust simulation environments, enabling the identification of effective control strategies even under noisy conditions. Selected agents are then validated on higher-fidelity simulations, illustrating how RL-based methods can reduce calibration overhead when compared to quantum optimal control techniques. Furthermore, the RL approach is hardware agnostic with the potential for broad applicability across various quantum computing platforms.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"22 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145813024","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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