Pub Date : 2020-11-13DOI: 10.21203/rs.3.rs-107899/v1
Jongmin Lee, G. Biedermann, John P. Mudrick, E. Douglas, Y. Jau
We present a demonstration of keeping a cold-atom ensemble within a sub-millimeter diameter hole in a transparent membrane.Based on the effective beam diameter of the magneto-optical trap (MOT) given by the hole diameter (d = 400 μm), we measurean atom number that is 105 times higher than the predicted value using the conventional d6 scaling rule. Atoms trapped bythe membrane MOT are cooled down to 10 μK with sub-Doppler cooling. Such a device can be potentially coupled to thephotonic/electronic integrated circuits that can be fabricated in the membrane device representing a step toward the atom trapintegrated platform.
{"title":"Membrane MOT: Trapping Dense Cold Atoms in a Sub-Millimeter Diameter Hole of a Microfabricated Membrane Device","authors":"Jongmin Lee, G. Biedermann, John P. Mudrick, E. Douglas, Y. Jau","doi":"10.21203/rs.3.rs-107899/v1","DOIUrl":"https://doi.org/10.21203/rs.3.rs-107899/v1","url":null,"abstract":"\u0000 We present a demonstration of keeping a cold-atom ensemble within a sub-millimeter diameter hole in a transparent membrane.Based on the effective beam diameter of the magneto-optical trap (MOT) given by the hole diameter (d = 400 μm), we measurean atom number that is 105 times higher than the predicted value using the conventional d6 scaling rule. Atoms trapped bythe membrane MOT are cooled down to 10 μK with sub-Doppler cooling. Such a device can be potentially coupled to thephotonic/electronic integrated circuits that can be fabricated in the membrane device representing a step toward the atom trapintegrated platform.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81909171","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}
Pub Date : 2020-11-12DOI: 10.1103/PhysRevA.104.042418
Kishor Bharti, T. Haug
Quantum simulation offers a possibility to explore the exponentially large configuration space of quantum mechanical systems and thus help us study poorly understood topics such as high-temperature superconductivity and drug design. Here, we provide a novel hybrid quantum-classical algorithm for simulating the dynamics of quantum systems. Without loss of generality, the Hamiltonian is assumed to be a linear combination of unitaries and the Ansatz wavefunction is taken as a linear combination of quantum states. The quantum states are fixed, and the combination parameters are variationally adjusted. Unlike existing variational quantum simulation algorithms, our algorithm does not require any classical-quantum feedback loop and by construction bypasses the barren plateau problem. Moreover, our algorithm does not require any complicated measurements, such as the Hadamard test. The entire framework is compatible with existing experimental capabilities and thus can be implemented immediately. We also provide an extension of our algorithm to imaginary time evolution.
{"title":"Quantum Assisted Simulator","authors":"Kishor Bharti, T. Haug","doi":"10.1103/PhysRevA.104.042418","DOIUrl":"https://doi.org/10.1103/PhysRevA.104.042418","url":null,"abstract":"Quantum simulation offers a possibility to explore the exponentially large configuration space of quantum mechanical systems and thus help us study poorly understood topics such as high-temperature superconductivity and drug design. Here, we provide a novel hybrid quantum-classical algorithm for simulating the dynamics of quantum systems. Without loss of generality, the Hamiltonian is assumed to be a linear combination of unitaries and the Ansatz wavefunction is taken as a linear combination of quantum states. The quantum states are fixed, and the combination parameters are variationally adjusted. Unlike existing variational quantum simulation algorithms, our algorithm does not require any classical-quantum feedback loop and by construction bypasses the barren plateau problem. Moreover, our algorithm does not require any complicated measurements, such as the Hadamard test. The entire framework is compatible with existing experimental capabilities and thus can be implemented immediately. We also provide an extension of our algorithm to imaginary time evolution.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77777726","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}
Pub Date : 2020-11-12DOI: 10.1103/PHYSREVRESEARCH.3.013037
M. Yamaguchi, A. Lyasota, T. Yuge
We propose a Makorvian quantum master equation that can describe the Fano effect directly, by assuming a standard cavity quantum electrodynamics system. The framework allows us to generalize the Fano formula, applicable over the weak and strong coupling regimes with pure dephasing. A formulation of its emission spectrum is also given in a consistent manner. We then find that the interference responsible for the Fano effect is robust against pure dephasing. This is counterintuitive because the impact of interference is, in general, severely reduced by decoherence processes. Our approach thus provides a basis for theoretical treatments of the Fano effect and new insights into the quantum interference in open quantum systems.
{"title":"Theory of Fano effect in cavity quantum electrodynamics","authors":"M. Yamaguchi, A. Lyasota, T. Yuge","doi":"10.1103/PHYSREVRESEARCH.3.013037","DOIUrl":"https://doi.org/10.1103/PHYSREVRESEARCH.3.013037","url":null,"abstract":"We propose a Makorvian quantum master equation that can describe the Fano effect directly, by assuming a standard cavity quantum electrodynamics system. The framework allows us to generalize the Fano formula, applicable over the weak and strong coupling regimes with pure dephasing. A formulation of its emission spectrum is also given in a consistent manner. We then find that the interference responsible for the Fano effect is robust against pure dephasing. This is counterintuitive because the impact of interference is, in general, severely reduced by decoherence processes. Our approach thus provides a basis for theoretical treatments of the Fano effect and new insights into the quantum interference in open quantum systems.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80557179","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}
Pub Date : 2020-11-11DOI: 10.1103/PHYSREVA.103.043704
Shi-fan Qi, J. Jing
Quantum conversion or interface is one of the most prominent protocols in quantum information processing and quantum state engineering. We propose a photon-phonon conversion protocol in a hybrid magnomechanical system comprising a microwave optical mode, a driven magnon mode and a mechanical-vibrating mode. The microwave photons in the optical cavity are coupled to the magnons by the magnetic-dipole interaction, and the latter are coupled to the mechanical phonons by the magnetostrictive interaction. With strong photon-magnon interaction and strong driving on magnon, an effective Hamiltonian is constructed to describe the conversion between photons and phonons nearby their resonant point. The cavity-magnon system can then play the role of a quantum memory. Moreover, the faithfulness of the photon-phonon conversion is estimated in terms of fidelities for state evolution and state-independent transfer. The former is discussed in the Lindblad master equation taking account the leakages of photon, phonon and magnon into consideration. The latter is derived by the Heisenberg-Langevin equation considering the non-Markovian noise from the structured environments for both optical and mechanical modes. The state-evolution fidelity is found to be robust to the weak leakage. The transfer fidelity can be maintained by the Ohmic and sub-Ohmic environments of the photons and is insensitive to the $1/f$ noise of the phonons. Our work thus provides an interesting application for the magnon system as a photon-phonon converter in the microwave regime.
{"title":"Magnon-assisted photon-phonon conversion in the presence of structured environments","authors":"Shi-fan Qi, J. Jing","doi":"10.1103/PHYSREVA.103.043704","DOIUrl":"https://doi.org/10.1103/PHYSREVA.103.043704","url":null,"abstract":"Quantum conversion or interface is one of the most prominent protocols in quantum information processing and quantum state engineering. We propose a photon-phonon conversion protocol in a hybrid magnomechanical system comprising a microwave optical mode, a driven magnon mode and a mechanical-vibrating mode. The microwave photons in the optical cavity are coupled to the magnons by the magnetic-dipole interaction, and the latter are coupled to the mechanical phonons by the magnetostrictive interaction. With strong photon-magnon interaction and strong driving on magnon, an effective Hamiltonian is constructed to describe the conversion between photons and phonons nearby their resonant point. The cavity-magnon system can then play the role of a quantum memory. Moreover, the faithfulness of the photon-phonon conversion is estimated in terms of fidelities for state evolution and state-independent transfer. The former is discussed in the Lindblad master equation taking account the leakages of photon, phonon and magnon into consideration. The latter is derived by the Heisenberg-Langevin equation considering the non-Markovian noise from the structured environments for both optical and mechanical modes. The state-evolution fidelity is found to be robust to the weak leakage. The transfer fidelity can be maintained by the Ohmic and sub-Ohmic environments of the photons and is insensitive to the $1/f$ noise of the phonons. Our work thus provides an interesting application for the magnon system as a photon-phonon converter in the microwave regime.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91463178","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}
Pub Date : 2020-11-11DOI: 10.1103/PhysRevA.103.052203
L. Mlodinow, T. Brun
Quantum walks on lattices can give rise to relativistic wave equations in the long-wavelength limit, but going beyond the single-particle case has proven challenging, especially in more than one spatial dimension. We construct quantum cellular automata for distinguishable particles based on two different quantum walks, and show that by restricting to the antisymmetric and symmetric subspaces, respectively, a multiparticle theory for free fermions and bosons in three spatial dimensions can be produced. This construction evades a no-go theorem that prohibits the usual fermionization constructions in more than one spatial dimension. In the long-wavelength limit, these recover Dirac field theory and Maxwell field theory, i.e., free QED.
{"title":"Fermionic and bosonic quantum field theories from quantum cellular automata in three spatial dimensions","authors":"L. Mlodinow, T. Brun","doi":"10.1103/PhysRevA.103.052203","DOIUrl":"https://doi.org/10.1103/PhysRevA.103.052203","url":null,"abstract":"Quantum walks on lattices can give rise to relativistic wave equations in the long-wavelength limit, but going beyond the single-particle case has proven challenging, especially in more than one spatial dimension. We construct quantum cellular automata for distinguishable particles based on two different quantum walks, and show that by restricting to the antisymmetric and symmetric subspaces, respectively, a multiparticle theory for free fermions and bosons in three spatial dimensions can be produced. This construction evades a no-go theorem that prohibits the usual fermionization constructions in more than one spatial dimension. In the long-wavelength limit, these recover Dirac field theory and Maxwell field theory, i.e., free QED.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77656589","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}
Pub Date : 2020-11-10DOI: 10.1103/PhysRevB.103.214308
V. Vadimov, J. Tuorila, Tuure Orell, J. Stockburger, T. Ala‐Nissila, J. Ankerhold, M. Möttönen
The urgent need for reliable simulation tools to match the extreme accuracy needed to control tailored quantum devices highlights the importance of understanding open quantum systems and their modeling. To this end, we compare here the commonly used Redfield and Lindblad master equations against numerically exact results in the case of one and two resonant qubits transversely coupled at a single point to a Drude-cut ohmic bath. All the relevant parameters are varied over a broad range which allows us to give detailed predictions about the validity and physically meaningful applicability of the weak-coupling approaches. We characterize the accuracy of the approximate approaches by comparing the maximum difference of their system evolution superoperators with numerically exact results. After optimizing the parameters of the approximate models to minimize the difference, we also explore if and to what extent the weak-coupling equations can be applied at least as phenomenological models. Optimization may lead to an accurate reproduction of experimental data, but yet our results are important to estimate the reliability of the extracted parameter values such as the bath temperature. Our findings set general guidelines for the range of validity of the usual Born-Markov master equations and indicate that they fail to accurately describe the physics in surprisingly broad range of parameters, in particular at low temperatures. Since quantum-technological devices operate there their accurate modeling calls for a careful choice of methods.
{"title":"Validity of Born-Markov master equations for single- and two-qubit systems","authors":"V. Vadimov, J. Tuorila, Tuure Orell, J. Stockburger, T. Ala‐Nissila, J. Ankerhold, M. Möttönen","doi":"10.1103/PhysRevB.103.214308","DOIUrl":"https://doi.org/10.1103/PhysRevB.103.214308","url":null,"abstract":"The urgent need for reliable simulation tools to match the extreme accuracy needed to control tailored quantum devices highlights the importance of understanding open quantum systems and their modeling. To this end, we compare here the commonly used Redfield and Lindblad master equations against numerically exact results in the case of one and two resonant qubits transversely coupled at a single point to a Drude-cut ohmic bath. All the relevant parameters are varied over a broad range which allows us to give detailed predictions about the validity and physically meaningful applicability of the weak-coupling approaches. We characterize the accuracy of the approximate approaches by comparing the maximum difference of their system evolution superoperators with numerically exact results. After optimizing the parameters of the approximate models to minimize the difference, we also explore if and to what extent the weak-coupling equations can be applied at least as phenomenological models. Optimization may lead to an accurate reproduction of experimental data, but yet our results are important to estimate the reliability of the extracted parameter values such as the bath temperature. Our findings set general guidelines for the range of validity of the usual Born-Markov master equations and indicate that they fail to accurately describe the physics in surprisingly broad range of parameters, in particular at low temperatures. Since quantum-technological devices operate there their accurate modeling calls for a careful choice of methods.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76088308","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}
Pub Date : 2020-11-10DOI: 10.1103/PHYSREVRESEARCH.3.013049
Carolyn E. Wood, M. Zych
Composite particles---atoms, molecules, or microspheres---are unique tools for testing joint quantum and general relativistic effects, macroscopic limits of quantum mechanics, and searching for new physics. However, all studies of the free propagation of these particles find that they delocalise into separate internal energy components, destroying their spatial coherence. This renders them unsuitable for experimental applications, as well as theoretical studies where they are used as idealised test masses or clocks. Here we solve this problem by introducing a new class of states with minimal uncertainty in space-time that fully overcome the delocalisation. The relevant physics comes from minimising the uncertainty between position and velocity, rather than position and momentum, while directly accounting for mass as an operator. Our results clarify the nature of composite particles, providing a currently missing theoretical tool with direct relevance for studies of joint foundations of quantum and relativistic phenomena, which removes a roadblock that could limit near-future quantum tests using composite particles.
{"title":"Composite particles with minimum uncertainty in spacetime","authors":"Carolyn E. Wood, M. Zych","doi":"10.1103/PHYSREVRESEARCH.3.013049","DOIUrl":"https://doi.org/10.1103/PHYSREVRESEARCH.3.013049","url":null,"abstract":"Composite particles---atoms, molecules, or microspheres---are unique tools for testing joint quantum and general relativistic effects, macroscopic limits of quantum mechanics, and searching for new physics. However, all studies of the free propagation of these particles find that they delocalise into separate internal energy components, destroying their spatial coherence. This renders them unsuitable for experimental applications, as well as theoretical studies where they are used as idealised test masses or clocks. Here we solve this problem by introducing a new class of states with minimal uncertainty in space-time that fully overcome the delocalisation. The relevant physics comes from minimising the uncertainty between position and velocity, rather than position and momentum, while directly accounting for mass as an operator. Our results clarify the nature of composite particles, providing a currently missing theoretical tool with direct relevance for studies of joint foundations of quantum and relativistic phenomena, which removes a roadblock that could limit near-future quantum tests using composite particles.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79706516","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}
Pub Date : 2020-11-09DOI: 10.1103/PRXQUANTUM.2.010103
R. Babbush, J. McClean, M. Newman, C. Gidney, S. Boixo, H. Neven
We discuss conditions under which it would be possible for a modest fault-tolerant quantum computer to realize a runtime advantage by executing a quantum algorithm with only a small polynomial speedup over the best classical alternative. The challenge is that the computation must finish within a reasonable amount of time while being difficult enough that the small quantum scaling advantage would compensate for the large constant factor overheads associated with error-correction. We compute several examples of such runtimes using state-of-the-art surface code constructions for superconducting qubits under a variety of assumptions. We conclude that quadratic speedups will not enable quantum advantage on early generations of such fault-tolerant devices unless there is a significant improvement in how we would realize quantum error-correction. While this conclusion persists even if we were to increase the rate of logical gates in the surface code by more than an order of magnitude, we also repeat this analysis for speedups by other polynomial degrees and find that quartic speedups look significantly more practical.
{"title":"Focus beyond Quadratic Speedups for Error-Corrected Quantum Advantage","authors":"R. Babbush, J. McClean, M. Newman, C. Gidney, S. Boixo, H. Neven","doi":"10.1103/PRXQUANTUM.2.010103","DOIUrl":"https://doi.org/10.1103/PRXQUANTUM.2.010103","url":null,"abstract":"We discuss conditions under which it would be possible for a modest fault-tolerant quantum computer to realize a runtime advantage by executing a quantum algorithm with only a small polynomial speedup over the best classical alternative. The challenge is that the computation must finish within a reasonable amount of time while being difficult enough that the small quantum scaling advantage would compensate for the large constant factor overheads associated with error-correction. We compute several examples of such runtimes using state-of-the-art surface code constructions for superconducting qubits under a variety of assumptions. We conclude that quadratic speedups will not enable quantum advantage on early generations of such fault-tolerant devices unless there is a significant improvement in how we would realize quantum error-correction. While this conclusion persists even if we were to increase the rate of logical gates in the surface code by more than an order of magnitude, we also repeat this analysis for speedups by other polynomial degrees and find that quartic speedups look significantly more practical.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75747685","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}
Pub Date : 2020-11-09DOI: 10.1103/PRXQuantum.2.020333
Ulysse Chabaud, G. Roeland, M. Walschaers, F. Grosshans, V. Parigi, D. Markham, N. Treps
We derive a theoretical framework for the experimental certification of non-Gaussian features of quantum states using double homodyne detection. We rank experimental non-Gaussian states according to the recently defined stellar hierarchy and we propose practical Wigner negativity witnesses. We simulate various use-cases ranging from fidelity estimation to witnessing Wigner negativity. Moreover, we extend results on the robustness of the stellar hierarchy of non-Gaussian states. Our results illustrate the usefulness of double homodyne detection as a practical measurement scheme for retrieving information about continuous variable quantum states.
{"title":"Certification of Non-Gaussian States with Operational Measurements","authors":"Ulysse Chabaud, G. Roeland, M. Walschaers, F. Grosshans, V. Parigi, D. Markham, N. Treps","doi":"10.1103/PRXQuantum.2.020333","DOIUrl":"https://doi.org/10.1103/PRXQuantum.2.020333","url":null,"abstract":"We derive a theoretical framework for the experimental certification of non-Gaussian features of quantum states using double homodyne detection. We rank experimental non-Gaussian states according to the recently defined stellar hierarchy and we propose practical Wigner negativity witnesses. We simulate various use-cases ranging from fidelity estimation to witnessing Wigner negativity. Moreover, we extend results on the robustness of the stellar hierarchy of non-Gaussian states. Our results illustrate the usefulness of double homodyne detection as a practical measurement scheme for retrieving information about continuous variable quantum states.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81699652","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：