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Super-exponential growth of out-of-time-ordered correlators 非时序相关器的超指数增长
arXiv: Quantum Physics Pub Date : 2020-12-04 DOI: 10.1103/PhysRevB.103.184311
Wen-Lei Zhao, Yue Hu, Zhi Li, Qian Wang
{"title":"Super-exponential growth of out-of-time-ordered correlators","authors":"Wen-Lei Zhao, Yue Hu, Zhi Li, Qian Wang","doi":"10.1103/PhysRevB.103.184311","DOIUrl":"https://doi.org/10.1103/PhysRevB.103.184311","url":null,"abstract":"Out-of-time-ordered correlators (OTOCs) are an effective tool in characterizing black hole chaos, many-body thermalization and quantum dynamics instability. Previous research findings have shown that the OTOCs' exponential growth (EG) marks the limit for quantum systems. However, we report in this letter a periodically-modulated nonlinear Schr\"odinger system, in which we interestingly find a novel way of information scrambling: super-EG. We show that the quantum OTOCs' growth, which stems from the quantum chaotic dynamics, will increase in a super-exponential way. We also find that in the classical limit, the hyper-chaos revealed by a linearly-increasing Lyapunov exponent actually triggers the super-EG of classical OTOCs. The results in this paper break the restraints of EG as the limit for quantum systems, which give us new insight into the nature of information scrambling in various fields of physics from black hole to many-body system.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78533799","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}
引用次数: 16
Improving phase estimation using number-conserving operations 利用保数运算改进相位估计
arXiv: Quantum Physics Pub Date : 2020-12-04 DOI: 10.1103/PhysRevA.103.052602
Huan Zhang, W. Ye, Chaoping Wei, Cun-jin Liu, Zeyang Liao, L. Hu
{"title":"Improving phase estimation using number-conserving operations","authors":"Huan Zhang, W. Ye, Chaoping Wei, Cun-jin Liu, Zeyang Liao, L. Hu","doi":"10.1103/PhysRevA.103.052602","DOIUrl":"https://doi.org/10.1103/PhysRevA.103.052602","url":null,"abstract":"We propose a theoretical scheme to improve the resolution and precision of phase measurement with parity detection in the Mach-Zehnder interferometer by using a nonclassical input state which is generated by applying a number-conserving generalized superposition of products (GSP) operation, (saa^{{dag}}+ta^{{dag}}a)^{m} with s^2+t^2=1, on two-mode squeezed vacuum (TMSV) state. The nonclassical properties of the proposed GSP-TMSV are investigated via average photon number (APN), anti-bunching effect, and degrees of two-mode squeezing. Particularly, our results show that both higher-order m GSP operation and smaller parameter s can increase the total APN, which leads to the improvement of quantum Fisher information. In addition, we also compare the phase measurement precision with and without photon losses between our scheme and the previous photon subtraction/addition schemes. It is found that our scheme, especially for the case of s=0, has the best performance via the enhanced phase resolution and sensitivity when comparing to those previous schemes even in the presence of photon losses. Interestingly, without losses, the standard quantum-noise limit (SQL) can always be surpassed in our our scheme and the Heisenberg limit (HL) can be even achieved when s=0.5,1 with small total APNs. However, in the presence of photon losses, the HL cannot be beaten, but the SQL can still be overcome particularly in the large total APN regimes. Our results here can find important applications in quantum metrology.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83703567","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}
引用次数: 7
Optimal tests for continuous-variable quantum teleportation and photodetectors 连续变量量子隐形传态和光电探测器的最佳测试
arXiv: Quantum Physics Pub Date : 2020-12-04 DOI: 10.1103/PhysRevResearch.4.023066
Kunal Sharma, B. Sanders, M. Wilde
{"title":"Optimal tests for continuous-variable quantum teleportation and photodetectors","authors":"Kunal Sharma, B. Sanders, M. Wilde","doi":"10.1103/PhysRevResearch.4.023066","DOIUrl":"https://doi.org/10.1103/PhysRevResearch.4.023066","url":null,"abstract":"Quantum teleportation is a primitive in several important applications, including quantum communication, quantum computation, error correction, and quantum networks. In this work, we propose an optimal test for the performance of continuous-variable (CV) quantum teleportation in terms of the energy-constrained channel fidelity between ideal CV teleportation and its experimental implementation. All work prior to ours considered suboptimal tests of the performance of CV teleportation, focusing instead on its performance for particular states, such as ensembles of coherent states, squeezed states, cat states, etc. Here we prove that the optimal state for testing CV teleportation is an entangled superposition of twin-Fock states. We establish this result by reducing the problem of estimating the energy-constrained channel fidelity between ideal CV teleportation and its experimental approximation to a quadratic program and solving it. As an additional result, we obtain an analytical solution to the energy-constrained diamond distance between a photodetector and its experimental approximation. These results are relevant for experiments that make use of CV teleportation and photodetectors.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87307506","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}
引用次数: 8
Variational optimization of the quantum annealing schedule for the Lechner-Hauke-Zoller scheme lechner - hake - zoller方案量子退火计划的变分优化
arXiv: Quantum Physics Pub Date : 2020-12-03 DOI: 10.1103/PHYSREVA.103.022619
Yuki Susa, H. Nishimori
{"title":"Variational optimization of the quantum annealing schedule for the Lechner-Hauke-Zoller scheme","authors":"Yuki Susa, H. Nishimori","doi":"10.1103/PHYSREVA.103.022619","DOIUrl":"https://doi.org/10.1103/PHYSREVA.103.022619","url":null,"abstract":"The annealing schedule is optimized for a parameter in the Lechner-Hauke-Zoller (LHZ) scheme for quantum annealing designed for the all-to-all-interacting Ising model representing generic combinatorial optimization problems. We adapt the variational approach proposed by Matsuura et al. (arXiv:2003.09913) to the annealing schedule of a term representing a constraint for variables intrinsic to the LHZ scheme. Numerical results for a simple ferromagnetic model and the spin glass problem show that non-monotonic annealing schedules optimize the performance measured by the residual energy and the final ground-state fidelity. This improvement does not accompany a notable increase in the instantaneous energy gap, which suggests the importance of a dynamical viewpoint in addition to static analyses in the study of practically-relevant diabatic processes in quantum annealing.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72903330","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}
引用次数: 11
Recycling qubits in near-term quantum computers 在近期量子计算机中回收量子位
arXiv: Quantum Physics Pub Date : 2020-12-03 DOI: 10.1103/PhysRevA.103.042613
Galit Anikeeva, Isaac H. Kim, P. Hayden
{"title":"Recycling qubits in near-term quantum computers","authors":"Galit Anikeeva, Isaac H. Kim, P. Hayden","doi":"10.1103/PhysRevA.103.042613","DOIUrl":"https://doi.org/10.1103/PhysRevA.103.042613","url":null,"abstract":"Quantum computers are capable of efficiently contracting unitary tensor networks, a task that is likely to remain difficult for classical computers. For instance, networks based on matrix product states or the multi-scale entanglement renormalization ansatz (MERA) can be contracted on a small quantum computer to aid the simulation of a large quantum system. However, without the ability to selectively reset qubits, the associated spatial cost can be exorbitant. In this paper, we propose a protocol that can unitarily reset qubits when the circuit has a common convolutional form, thus dramatically reducing the spatial cost for implementing the contraction algorithm on general near-term quantum computers. This protocol generates fresh qubits from used ones by partially applying the time-reversed quantum circuit over qubits that are no longer in use. In the absence of noise, we prove that the state of a subset of these qubits becomes $|0ldots 0rangle$, up to an error exponentially small in the number of gates applied. We also provide a numerical evidence that the protocol works in the presence of noise.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74513294","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}
引用次数: 6
Fully Quantum Scalable Description of Driven-Dissipative Lattice Models 驱动耗散晶格模型的全量子可伸缩描述
arXiv: Quantum Physics Pub Date : 2020-12-03 DOI: 10.1103/PRXQUANTUM.2.010319
P. Deuar, A. Ferrier, M. Matuszewski, G. Orso, M. Szyma'nska
{"title":"Fully Quantum Scalable Description of Driven-Dissipative Lattice Models","authors":"P. Deuar, A. Ferrier, M. Matuszewski, G. Orso, M. Szyma'nska","doi":"10.1103/PRXQUANTUM.2.010319","DOIUrl":"https://doi.org/10.1103/PRXQUANTUM.2.010319","url":null,"abstract":"Methods for modeling large driven dissipative quantum systems are becoming increasingly urgent due to recent experimental progress in a number of photonic platforms. We demonstrate the positive-P method to be ideal for this purpose across a wide range of parameters, focusing on the archetypal driven dissipative Bose-Hubbard model. Notably, these parameters include intermediate regimes where interactions and dissipation are comparable, and especially cases with low occupations for which common semiclassical approximations can break down. The presence of dissipation can alleviate instabilities in the method that are known to occur for closed systems, allowing the simulation of dynamics up to and including the steady state. Throughout the parameter space of the model, we determine the magnitude of dissipation that is sufficient to make the method useful and stable, finding its region of applicability to be complementary to that of truncated Wigner. We then demonstrate its use in a number of examples with nontrivial quantum correlations, including a demonstration of solving the urgent open problem of large and highly non-uniform systems with even tens of thousands of sites.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81180290","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}
引用次数: 13
Perturbative algorithm for rotational decoherence 旋转退相干的微扰算法
arXiv: Quantum Physics Pub Date : 2020-12-02 DOI: 10.1103/PHYSREVA.103.032220
M. Carlesso, H. Naeij, A. Bassi
{"title":"Perturbative algorithm for rotational decoherence","authors":"M. Carlesso, H. Naeij, A. Bassi","doi":"10.1103/PHYSREVA.103.032220","DOIUrl":"https://doi.org/10.1103/PHYSREVA.103.032220","url":null,"abstract":"Recent advances in levitated optomechanics provide new perspectives for the use of rotational degrees of freedom for the development of quantum technologies as well as for testing fundamental physics. As for the translational case, their use, especially in the quantum regime, is limited by environmental noises, whose characterization is fundamental in order to assess, control and minimize their effect, in particular decoherence. Here, we present a general perturbative approach to compute decoherence for a quantum system in a superposition of its rotational degrees of freedom. The specific cases of the dipole-dipole and quadrupole-quadrupole interactions are solved explicitly, and we show that the rotational degrees of freedom decohere on a time scale that is longer than the translational one.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79762951","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}
引用次数: 2
Transmon in a semi-infinite high-impedance transmission line: Appearance of cavity modes and Rabi oscillations 半无限高阻抗传输线中的传输子:腔模和拉比振荡的出现
arXiv: Quantum Physics Pub Date : 2020-12-02 DOI: 10.1103/PHYSREVRESEARCH.3.023003
E. Wiegand, B. Rousseaux, G. Johansson
{"title":"Transmon in a semi-infinite high-impedance transmission line: Appearance of cavity modes and Rabi oscillations","authors":"E. Wiegand, B. Rousseaux, G. Johansson","doi":"10.1103/PHYSREVRESEARCH.3.023003","DOIUrl":"https://doi.org/10.1103/PHYSREVRESEARCH.3.023003","url":null,"abstract":"In this letter, we investigate the dynamics of a single superconducting artificial atom capacitively coupled to a transmission line with a characteristic impedance comparable or larger than the quantum resistance. In this regime, microwaves are reflected from the atom also at frequencies far from the atom's transition frequency. Adding a single mirror in the transmission line then creates cavity modes between the atom and the mirror. Investigating the spontaneous emission from the atom, we then find Rabi oscillations, where the energy oscillates between the atom and one of the cavity modes.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90753853","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}
引用次数: 3
Satellite-Based Photonic Quantum Networks Are Small-World 基于卫星的光子量子网络是小世界的
arXiv: Quantum Physics Pub Date : 2020-12-02 DOI: 10.1103/PRXQUANTUM.2.010304
S. Brito, A. Canabarro, D. Cavalcanti, R. Chaves
{"title":"Satellite-Based Photonic Quantum Networks Are Small-World","authors":"S. Brito, A. Canabarro, D. Cavalcanti, R. Chaves","doi":"10.1103/PRXQUANTUM.2.010304","DOIUrl":"https://doi.org/10.1103/PRXQUANTUM.2.010304","url":null,"abstract":"Recent milestone experiments establishing satellite-to-ground quantum communication are paving the way for the development of the quantum internet, a network interconnected by quantum channels. Here we employ network theory to study the properties of the photonic networks that can be generated by satellite-based quantum communication and compare it with the optical-fiber counterpart. We predict that satellites can generate small-world networks, implying that physically distant nodes are actually near from a network perspective. We also analyse the connectivity properties of the network and show, in particular, that they are robust against random failures. This puts satellite-based quantum communication as the most promising technology to distribute entanglement across large distances in quantum networks of growing size and complexity.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80553996","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}
引用次数: 18
Quantum dynamics under continuous projective measurements: Non-Hermitian description and the continuum-space limit 连续射影测量下的量子动力学:非厄米描述和连续空间极限
arXiv: Quantum Physics Pub Date : 2020-12-02 DOI: 10.1103/PHYSREVA.103.032221
V. Dubey, C. Bernardin, A. Dhar
{"title":"Quantum dynamics under continuous projective measurements: Non-Hermitian description and the continuum-space limit","authors":"V. Dubey, C. Bernardin, A. Dhar","doi":"10.1103/PHYSREVA.103.032221","DOIUrl":"https://doi.org/10.1103/PHYSREVA.103.032221","url":null,"abstract":"The problem of the time of arrival of a quantum system in a specified state is considered in the framework of the repeated measurement protocol and in particular the limit of continuous measurements is discussed. It is shown that for a particular choice of system-detector coupling, the Zeno effect is avoided and the system can be described effectively by a non-Hermitian effective Hamiltonian. As a specific example we consider the evolution of a quantum particle on a one-dimensional lattice that is subjected to position measurements at a specific site. By solving the corresponding non-Hermitian wave function evolution equation, we present analytic closed-form results on the survival probability and the first arrival time distribution. Finally we discuss the limit of vanishing lattice spacing and show that this leads to a continuum description where the particle evolves via the free Schrodinger equation with complex Robin boundary conditions at the detector site. Several interesting physical results for this dynamics are presented.","PeriodicalId":8484,"journal":{"name":"arXiv: Quantum Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89402029","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}
引用次数: 17
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