Orkash Amat, Hong-Hao Fan, Suo Tang, Yong-Feng Huang, Bai-Song Xie
We have formulated a generalized two level model for studying the pair production in multidimensional time-dependent electric fields. It can provide momentum spectra with fully spin resolved components for all possible combined spin states of the particle and anti-particle simultaneously. Moreover, we have also investigated the validity of the two level model for fermions (scalar particles) by comparing the results with those by equal-time Dirac-Heisenberg-Wigner (Feshbach-Villars-Heisenberg-Wigner) formalism in different regimes of pair creation, i.e., multiphoton and tunneling dominated mechanisms. It is found that the results are consistent with each other, indicating the good approximation of the two level model. In particular, in terms of the two level model, we found that the contribution of the particle momentum spectra is the greatest when the spin states of the particle and anti-particle are parallel with $S=1$. It is believed that by this two level model one can extend researches on pair production for more different background fields, such as a slowly varying spatial-temporal one. Many other interesting phenomena may also be revealed, including the spin-resolved vortex structure that is contained in the phase feature of the distribution function of the created pairs.
{"title":"Spin resolved momentum spectra for vacuum pair production via a generalized two level model","authors":"Orkash Amat, Hong-Hao Fan, Suo Tang, Yong-Feng Huang, Bai-Song Xie","doi":"arxiv-2409.11833","DOIUrl":"https://doi.org/arxiv-2409.11833","url":null,"abstract":"We have formulated a generalized two level model for studying the pair\u0000production in multidimensional time-dependent electric fields. It can provide\u0000momentum spectra with fully spin resolved components for all possible combined\u0000spin states of the particle and anti-particle simultaneously. Moreover, we have\u0000also investigated the validity of the two level model for fermions (scalar\u0000particles) by comparing the results with those by equal-time\u0000Dirac-Heisenberg-Wigner (Feshbach-Villars-Heisenberg-Wigner) formalism in\u0000different regimes of pair creation, i.e., multiphoton and tunneling dominated\u0000mechanisms. It is found that the results are consistent with each other,\u0000indicating the good approximation of the two level model. In particular, in\u0000terms of the two level model, we found that the contribution of the particle\u0000momentum spectra is the greatest when the spin states of the particle and\u0000anti-particle are parallel with $S=1$. It is believed that by this two level\u0000model one can extend researches on pair production for more different\u0000background fields, such as a slowly varying spatial-temporal one. Many other\u0000interesting phenomena may also be revealed, including the spin-resolved vortex\u0000structure that is contained in the phase feature of the distribution function\u0000of the created pairs.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":"48 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142248114","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Romain Dalidet, Anthony Martin, Grégory Sauder, Laurent Labonté, Sébastien Tanzilli
Quantum interferometry methods exploit quantum resources, such as photonic entanglement, to enhance phase estimation beyond classical limits. Nonlinear optics has served as a workhorse for the generation of entangled photon pairs, ensuring both energy and phase conservation, but at the cost of limited rate and degraded signal-to-noise ratio compared to laser-based interferometry approaches. We present a "quantum-like" nonlinear optical method that reaches super-resolution in single-photon detection regime. This is achieved by replacing photon-pairs by coherent states of light, mimicking quantum properties through classical nonlinear optics processes. Our scheme utilizes two high-brightness lasers. This results in a substantially greater signal-to-noise ratio compared to its quantum counterpart. Such an approach paves the way to significantly reduced acquisition times, providing a pathway to explore signals across a broader range of bandwidth. The need to increase the frequency bandwidth of the quantum sensor significantly motivates the potential applications of this pathway.
{"title":"Quantum-like nonlinear interferometry with frequency-engineered classical light","authors":"Romain Dalidet, Anthony Martin, Grégory Sauder, Laurent Labonté, Sébastien Tanzilli","doi":"arxiv-2409.12049","DOIUrl":"https://doi.org/arxiv-2409.12049","url":null,"abstract":"Quantum interferometry methods exploit quantum resources, such as photonic\u0000entanglement, to enhance phase estimation beyond classical limits. Nonlinear\u0000optics has served as a workhorse for the generation of entangled photon pairs,\u0000ensuring both energy and phase conservation, but at the cost of limited rate\u0000and degraded signal-to-noise ratio compared to laser-based interferometry\u0000approaches. We present a \"quantum-like\" nonlinear optical method that reaches\u0000super-resolution in single-photon detection regime. This is achieved by\u0000replacing photon-pairs by coherent states of light, mimicking quantum\u0000properties through classical nonlinear optics processes. Our scheme utilizes\u0000two high-brightness lasers. This results in a substantially greater\u0000signal-to-noise ratio compared to its quantum counterpart. Such an approach\u0000paves the way to significantly reduced acquisition times, providing a pathway\u0000to explore signals across a broader range of bandwidth. The need to increase\u0000the frequency bandwidth of the quantum sensor significantly motivates the\u0000potential applications of this pathway.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":"9 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142248075","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zichang He, David Amaro, Ruslan Shaydulin, Marco Pistoia
Quantum algorithms must be scaled up to tackle real-world applications. Doing so requires overcoming the noise present on today's hardware. The quantum approximate optimization algorithm (QAOA) is a promising candidate for scaling up due to its modest resource requirements and documented asymptotic speedup over state-of-the-art classical algorithms for some problems. However, achieving better-than-classical performance with QAOA is believed to require fault tolerance. In this paper, we demonstrate a partially fault-tolerant implementation of QAOA using the $[[k+2,k,2]]$ ``Iceberg'' error detection code. We observe that encoding the circuit with the Iceberg code improves the algorithmic performance as compared to the unencoded circuit for problems with up to $20$ logical qubits on a trapped-ion quantum computer. Additionally, we propose and calibrate a model for predicting the code performance, and use it to characterize the limits of the Iceberg code and extrapolate its performance to future hardware with improved error rates. In particular, we show how our model can be used to determine necessary conditions for QAOA to outperform Goemans-Williamson algorithm on future hardware. Our results demonstrate the largest universal quantum computing algorithm protected by partially fault-tolerant quantum error detection on practical applications to date, paving the way towards solving real-world applications with quantum computers.
{"title":"Performance of Quantum Approximate Optimization with Quantum Error Detection","authors":"Zichang He, David Amaro, Ruslan Shaydulin, Marco Pistoia","doi":"arxiv-2409.12104","DOIUrl":"https://doi.org/arxiv-2409.12104","url":null,"abstract":"Quantum algorithms must be scaled up to tackle real-world applications. Doing\u0000so requires overcoming the noise present on today's hardware. The quantum\u0000approximate optimization algorithm (QAOA) is a promising candidate for scaling\u0000up due to its modest resource requirements and documented asymptotic speedup\u0000over state-of-the-art classical algorithms for some problems. However,\u0000achieving better-than-classical performance with QAOA is believed to require\u0000fault tolerance. In this paper, we demonstrate a partially fault-tolerant\u0000implementation of QAOA using the $[[k+2,k,2]]$ ``Iceberg'' error detection\u0000code. We observe that encoding the circuit with the Iceberg code improves the\u0000algorithmic performance as compared to the unencoded circuit for problems with\u0000up to $20$ logical qubits on a trapped-ion quantum computer. Additionally, we\u0000propose and calibrate a model for predicting the code performance, and use it\u0000to characterize the limits of the Iceberg code and extrapolate its performance\u0000to future hardware with improved error rates. In particular, we show how our\u0000model can be used to determine necessary conditions for QAOA to outperform\u0000Goemans-Williamson algorithm on future hardware. Our results demonstrate the\u0000largest universal quantum computing algorithm protected by partially\u0000fault-tolerant quantum error detection on practical applications to date,\u0000paving the way towards solving real-world applications with quantum computers.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":"59 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142268298","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Qudit-based quantum gates in high-dimensional Hilbert space can provide a viable route towards effectively accelerating the speed of quantum computing and performing complex quantum logic operations. In the paper, we propose a 2-qudit $4times4$-dimensional controlled-not (CNOT) gate for four silicon-vacancy spins, in which the first two electron-spin states in silicon-vacancy centers are encoded as the control qudits, and the other ones as the target qudits. The proposed protocol is implemented with assistance of an ancillary photon that serves as a common-data bus linking four motionless silicon-vacancy spins placed in four independent single-sided optical nanocavities. Moreover, the CNOT gate works in a deterministic manner by performing the relational feed-forward operations corresponding to the diverse outcomes of the single-photon detectors to be directed against the ancillary photon. Further, it can be potentially generalized to other solid-state quantum system. Under current technological conditions, both the efficiency and fidelity of the 2-qudit CNOT gate are high.
{"title":"A Computation-Enhanced High-Dimensional Quantum Gate for Silicon-Vacancy Spins","authors":"Gang Fan, Fang-Fang Du","doi":"arxiv-2409.11757","DOIUrl":"https://doi.org/arxiv-2409.11757","url":null,"abstract":"Qudit-based quantum gates in high-dimensional Hilbert space can provide a\u0000viable route towards effectively accelerating the speed of quantum computing\u0000and performing complex quantum logic operations. In the paper, we propose a\u00002-qudit $4times4$-dimensional controlled-not (CNOT) gate for four\u0000silicon-vacancy spins, in which the first two electron-spin states in\u0000silicon-vacancy centers are encoded as the control qudits, and the other ones\u0000as the target qudits. The proposed protocol is implemented with assistance of\u0000an ancillary photon that serves as a common-data bus linking four motionless\u0000silicon-vacancy spins placed in four independent single-sided optical\u0000nanocavities. Moreover, the CNOT gate works in a deterministic manner by\u0000performing the relational feed-forward operations corresponding to the diverse\u0000outcomes of the single-photon detectors to be directed against the ancillary\u0000photon. Further, it can be potentially generalized to other solid-state quantum\u0000system. Under current technological conditions, both the efficiency and\u0000fidelity of the 2-qudit CNOT gate are high.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":"46 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142248101","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We study a center-of-mass-conserving Brownian complex Sachdev-Ye-Kitaev model with long-range (power-law) interactions characterized by $1/r^eta$. The kinetic constraint and long-range interactions conspire to yield rich hydrodynamics associated with the conserved charge, which we reveal by computing the Schwinger-Keldysh effective action. Our result shows that charge transport in this system can be subdiffusive, diffusive, or superdiffusive, with the dynamical exponent controlled by $eta$. We further employ a doubled Hilbert space methodology to derive an effective action for the out-of-time-order correlator (OTOC), from which we obtain the phase diagram delineating regimes where the lightcone is linear or logarithmic. Our results provide a concrete example of a quantum many-body system with kinetic constraint and long-range interactions in which the emergent hydrodynamic modes and OTOC can be computed analytically.
{"title":"Hydrodynamic modes and operator spreading in a long-range center-of-mass-conserving Brownian SYK model","authors":"Bai-Lin Cheng, Shao-Kai Jian, Zhi-Cheng Yang","doi":"arxiv-2409.11655","DOIUrl":"https://doi.org/arxiv-2409.11655","url":null,"abstract":"We study a center-of-mass-conserving Brownian complex Sachdev-Ye-Kitaev model\u0000with long-range (power-law) interactions characterized by $1/r^eta$. The\u0000kinetic constraint and long-range interactions conspire to yield rich\u0000hydrodynamics associated with the conserved charge, which we reveal by\u0000computing the Schwinger-Keldysh effective action. Our result shows that charge\u0000transport in this system can be subdiffusive, diffusive, or superdiffusive,\u0000with the dynamical exponent controlled by $eta$. We further employ a doubled\u0000Hilbert space methodology to derive an effective action for the\u0000out-of-time-order correlator (OTOC), from which we obtain the phase diagram\u0000delineating regimes where the lightcone is linear or logarithmic. Our results\u0000provide a concrete example of a quantum many-body system with kinetic\u0000constraint and long-range interactions in which the emergent hydrodynamic modes\u0000and OTOC can be computed analytically.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142248116","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Archak Purkayastha, Giacomo Guarnieri, Janet Anders, Marco Merkli
Thermalization of isolated and open quantum systems has been studied extensively. However, being the subject of investigation by different scientific communities and being analysed using different mathematical tools, the connection between the isolated (IQS) and open (OQS) approaches to thermalization has remained opaque. Here we demonstrate that the fundamental difference between the two paradigms is the order in which the long time and the thermodynamic limits are taken. This difference implies that they describe physics on widely different time and length scales. Our analysis is carried out numerically for the case of a double quantum dot (DQD) coupled to a fermionic lead. We show how both OQS and IQS thermalization can be explored in this model on equal footing, allowing a fair comparison between the two. We find that while the quadratically coupled (free) DQD experiences no isolated thermalization, it of course does experience open thermalization. For the non-linearly interacting DQD coupled to fermionic lead, we show by characterizing its spectral form factor and level spacing distribution, that the system falls in the twilight zone between integrable and non-integrable regimes, which we call partially non-integrable. We further evidence that, despite being only partially non-integrable and thereby falling outside the remit of the standard eigenstate thermalization hypothesis, it nevertheless experiences IQS as well as OQS thermalization.
{"title":"On the difference between thermalization in open and isolated quantum systems: a case study","authors":"Archak Purkayastha, Giacomo Guarnieri, Janet Anders, Marco Merkli","doi":"arxiv-2409.11932","DOIUrl":"https://doi.org/arxiv-2409.11932","url":null,"abstract":"Thermalization of isolated and open quantum systems has been studied\u0000extensively. However, being the subject of investigation by different\u0000scientific communities and being analysed using different mathematical tools,\u0000the connection between the isolated (IQS) and open (OQS) approaches to\u0000thermalization has remained opaque. Here we demonstrate that the fundamental\u0000difference between the two paradigms is the order in which the long time and\u0000the thermodynamic limits are taken. This difference implies that they describe\u0000physics on widely different time and length scales. Our analysis is carried out\u0000numerically for the case of a double quantum dot (DQD) coupled to a fermionic\u0000lead. We show how both OQS and IQS thermalization can be explored in this model\u0000on equal footing, allowing a fair comparison between the two. We find that\u0000while the quadratically coupled (free) DQD experiences no isolated\u0000thermalization, it of course does experience open thermalization. For the\u0000non-linearly interacting DQD coupled to fermionic lead, we show by\u0000characterizing its spectral form factor and level spacing distribution, that\u0000the system falls in the twilight zone between integrable and non-integrable\u0000regimes, which we call partially non-integrable. We further evidence that,\u0000despite being only partially non-integrable and thereby falling outside the\u0000remit of the standard eigenstate thermalization hypothesis, it nevertheless\u0000experiences IQS as well as OQS thermalization.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":"43 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142248109","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Macroscopic QED (MQED) is the field theory for computing quantum electromagnetic effects in dispersive media. Here we extend MQD to treat time-varying, dispersive media. For a time dependent Drude model, we find that the expected replacement ${epsilon}({omega}) {to} {epsilon}(t,{omega})$ within standard MQED leads to nonphysical polarization currents, becoming singular in the limit of a step change in the carrier density. We show this singular behaviour can be removed through modifying the reservaoir dynamics, quantizing the resulting theory and finding the non-equilibrium, time-varying noise currents, which exhibit extra correlations due to temporal reflections within the material dynamics.
{"title":"Macroscopic QED and noise currents in time-varying media","authors":"S. A. R. Horsley, B. Baker","doi":"arxiv-2409.11873","DOIUrl":"https://doi.org/arxiv-2409.11873","url":null,"abstract":"Macroscopic QED (MQED) is the field theory for computing quantum\u0000electromagnetic effects in dispersive media. Here we extend MQD to treat\u0000time-varying, dispersive media. For a time dependent Drude model, we find that\u0000the expected replacement ${epsilon}({omega}) {to} {epsilon}(t,{omega})$\u0000within standard MQED leads to nonphysical polarization currents, becoming\u0000singular in the limit of a step change in the carrier density. We show this\u0000singular behaviour can be removed through modifying the reservaoir dynamics,\u0000quantizing the resulting theory and finding the non-equilibrium, time-varying\u0000noise currents, which exhibit extra correlations due to temporal reflections\u0000within the material dynamics.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142248112","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We design flexible fault tolerant gate gadgets that allow the data and the ancilla to be encoded using different codes. By picking a stabilizer code for the ancilla we are able to perform both Clifford and non-Clifford gates fault tolerantly on generic quantum codes, including both stabilizer and non-additive codes. This allows us to demonstrate the first universal fault tolerant gate set for non-additive codes. We consider fault tolerance both with respect to a dephasing channel and a depolarizing channel.
{"title":"Flexible Fault Tolerant Gate Gadgets","authors":"Eric Kubischta, Ian Teixeira","doi":"arxiv-2409.11616","DOIUrl":"https://doi.org/arxiv-2409.11616","url":null,"abstract":"We design flexible fault tolerant gate gadgets that allow the data and the\u0000ancilla to be encoded using different codes. By picking a stabilizer code for\u0000the ancilla we are able to perform both Clifford and non-Clifford gates fault\u0000tolerantly on generic quantum codes, including both stabilizer and non-additive\u0000codes. This allows us to demonstrate the first universal fault tolerant gate\u0000set for non-additive codes. We consider fault tolerance both with respect to a\u0000dephasing channel and a depolarizing channel.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142248107","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Atoms excited to Rydberg states have recently emerged as a valuable resource in neutral atom platforms for quantum computation, quantum simulation, and quantum information processing. Atoms in Rydberg states have large polarizabilities, making them highly sensitive to electric fields. Therefore, stray electric fields can decohere these atoms, in addition to compromising the fidelity of engineered interactions between them. It is therefore essential to cancel these stray electric fields. Here we present a novel, simple, and highly-compact electrode assembly, implemented in a glass cell-based vacuum chamber design, for stray electric field cancellation. The electrode assembly allows for full 3D control of the electric field in the vicinity of the atoms while blocking almost no optical access. We experimentally demonstrate the cancellation of stray electric fields to better than 10 mV/cm using this electrode assembly.
{"title":"Electric field control for experiments with atoms in Rydberg states","authors":"Aishik Panja, Yupeng Wang, Xinghan Wang, Junjie Wang, Sarthak Subhankar, Qi-Yu Liang","doi":"arxiv-2409.11865","DOIUrl":"https://doi.org/arxiv-2409.11865","url":null,"abstract":"Atoms excited to Rydberg states have recently emerged as a valuable resource\u0000in neutral atom platforms for quantum computation, quantum simulation, and\u0000quantum information processing. Atoms in Rydberg states have large\u0000polarizabilities, making them highly sensitive to electric fields. Therefore,\u0000stray electric fields can decohere these atoms, in addition to compromising the\u0000fidelity of engineered interactions between them. It is therefore essential to\u0000cancel these stray electric fields. Here we present a novel, simple, and\u0000highly-compact electrode assembly, implemented in a glass cell-based vacuum\u0000chamber design, for stray electric field cancellation. The electrode assembly\u0000allows for full 3D control of the electric field in the vicinity of the atoms\u0000while blocking almost no optical access. We experimentally demonstrate the\u0000cancellation of stray electric fields to better than 10 mV/cm using this\u0000electrode assembly.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":"13 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142248111","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dominic W. Berry, Yu Tong, Tanuj Khattar, Alec White, Tae In Kim, Sergio Boixo, Lin Lin, Seunghoon Lee, Garnet Kin-Lic Chan, Ryan Babbush, Nicholas C. Rubin
Studies on quantum algorithms for ground state energy estimation often assume perfect ground state preparation; however, in reality the initial state will have imperfect overlap with the true ground state. Here we address that problem in two ways: by faster preparation of matrix product state (MPS) approximations, and more efficient filtering of the prepared state to find the ground state energy. We show how to achieve unitary synthesis with a Toffoli complexity about $7 times$ lower than that in prior work, and use that to derive a more efficient MPS preparation method. For filtering we present two different approaches: sampling and binary search. For both we use the theory of window functions to avoid large phase errors and minimise the complexity. We find that the binary search approach provides better scaling with the overlap at the cost of a larger constant factor, such that it will be preferred for overlaps less than about $0.003$. Finally, we estimate the total resources to perform ground state energy estimation of Fe-S cluster systems, including the FeMo cofactor by estimating the overlap of different MPS initial states with potential ground-states of the FeMo cofactor using an extrapolation procedure. {With a modest MPS bond dimension of 4000, our procedure produces an estimate of $sim 0.9$ overlap squared with a candidate ground-state of the FeMo cofactor, producing a total resource estimate of $7.3 times 10^{10}$ Toffoli gates; neglecting the search over candidates and assuming the accuracy of the extrapolation, this validates prior estimates that used perfect ground state overlap. This presents an example of a practical path to prepare states of high overlap in a challenging-to-compute chemical system.
{"title":"Rapid initial state preparation for the quantum simulation of strongly correlated molecules","authors":"Dominic W. Berry, Yu Tong, Tanuj Khattar, Alec White, Tae In Kim, Sergio Boixo, Lin Lin, Seunghoon Lee, Garnet Kin-Lic Chan, Ryan Babbush, Nicholas C. Rubin","doi":"arxiv-2409.11748","DOIUrl":"https://doi.org/arxiv-2409.11748","url":null,"abstract":"Studies on quantum algorithms for ground state energy estimation often assume\u0000perfect ground state preparation; however, in reality the initial state will\u0000have imperfect overlap with the true ground state. Here we address that problem\u0000in two ways: by faster preparation of matrix product state (MPS)\u0000approximations, and more efficient filtering of the prepared state to find the\u0000ground state energy. We show how to achieve unitary synthesis with a Toffoli\u0000complexity about $7 times$ lower than that in prior work, and use that to\u0000derive a more efficient MPS preparation method. For filtering we present two\u0000different approaches: sampling and binary search. For both we use the theory of\u0000window functions to avoid large phase errors and minimise the complexity. We\u0000find that the binary search approach provides better scaling with the overlap\u0000at the cost of a larger constant factor, such that it will be preferred for\u0000overlaps less than about $0.003$. Finally, we estimate the total resources to\u0000perform ground state energy estimation of Fe-S cluster systems, including the\u0000FeMo cofactor by estimating the overlap of different MPS initial states with\u0000potential ground-states of the FeMo cofactor using an extrapolation procedure.\u0000{With a modest MPS bond dimension of 4000, our procedure produces an estimate\u0000of $sim 0.9$ overlap squared with a candidate ground-state of the FeMo\u0000cofactor, producing a total resource estimate of $7.3 times 10^{10}$ Toffoli\u0000gates; neglecting the search over candidates and assuming the accuracy of the\u0000extrapolation, this validates prior estimates that used perfect ground state\u0000overlap. This presents an example of a practical path to prepare states of high\u0000overlap in a challenging-to-compute chemical system.","PeriodicalId":501226,"journal":{"name":"arXiv - PHYS - Quantum Physics","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142248104","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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