We show that all geometric quantum gates (GQG's in short), which are quantum gates only with geometric phases, are robust against control field strength errors. As examples of this observation, we show (1) how robust composite rf-pulses in NMR are geometrically constructed and (2) a composite rf-pulse based on Trotter-Suzuki Formulas is a GQG.
In this paper, we investigate a thermal coherent state defined with the Lie-Trotter product formula under the formalism of the thermo field dynamics. In the definition of our thermal coherent state, we treat the thermalizing operator and the displacement operator symmetrically. We examine its uncertainty relation and quasiprobability distributions. Although this thermal coherent state is equivalent to the conventional ones except for different parameterizations and a phase factor, it is convenient for describing an experimental setup of the optical parametric oscillator laser.
Quantum simulation promises to address many challenges in fields ranging from quantum chemistry to material science, and high-energy physics, and could be implemented in noisy intermediate-scale quantum devices. A challenge in building good digital quantum simulators is the fidelity of the engineered dynamics given a finite set of elementary operations. Here we present a framework for optimizing the order of operations based on a geometric picture, thus abstracting from the operation details and achieving computational efficiency. Based on this geometric framework, we provide two alternative s…
We study path integrals in the Trotter-type form for the Schrödinger equation, where the Hamiltonian is the Weyl quantization of a real-valued quadratic form perturbed by a potential $V$ in a class encompassing that - considered by Albeverio and Itô in celebrated papers - of Fourier transforms of complex measures. Essentially, $V$ is bounded and has the regularity of a function whose Fourier transform is in $L^1$. Whereas the strong convergence in $L^2$ in the Trotter formula, as well as several related issues at the operator norm level are well understood, the original Feynman's idea concerne…
Unbiased Hamiltonian Simulation by Reversing Trotter Error Dynamics
Quantinuum K.K.;Department of Physics, The University of Tokyo(东京大学物理学系);RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)(理化学研究所交叉理论与数学科学中心 (iTHEMS));RIKEN(理化学研究所);Quantinuum;Institute for Physics of Intelligence, The University of Tokyo(东京大学物理智能研究所);Institute for Solid State Physics, The University of Tokyo(东京大学固体物理研究所)
We consider the relation between so called continuous localization models - i.e. non-linear stochastic Schrödinger evolutions - and the discrete GRW-model of wave function collapse. The former can be understood as scaling limit of the GRW process. The proof relies on a stochastic Trotter formula, which is of interest in its own right. Our Trotter formula also allows to complement results on existence theory of stochastic Schrödinger evolutions by Holevo and Mora/Rebolledo.
Beyond Trotterization: Variational Product Formulas for Quantum Simulation
Memorial University of Newfoundland and Labrador(纽芬兰与拉布拉多纪念大学);Interdisciplinary Research Center (IRC) for Advanced Quantum Computing (AQC)(先进量子计算跨学科研究中心);National Research Council Canada(加拿大国家研究委员会);Perimeter Institute for Theoretical Physics(理论物理 perimeter 研究所);Institute for Quantum Computing(量子计算研究所);Compute Everything Technologies Ltd.(Compute Everything 科技有限公司)
We consider the dynamics $t\mapstoτ_t$ of an infinite quantum lattice system that is generated by a local interaction. If the interaction decomposes into a finite number of terms that are themselves local interactions, we show that $τ_t$ can be efficiently approximated by a product of $n$ automorphisms, each of them being an alternating product generated by the individual terms. For any integer $m$, we construct a product formula (in the spirit of Trotter) such that the approximation error scales as $n^{-m}$. Our bounds hold in norm, pointwise for algebra elements that are sufficiently well ap…
We consider Hamiltonian simulation using the first order Lie-Trotter product formula under the assumption that the initial state has a high overlap with an energy eigenstate, or a collection of eigenstates in a narrow energy band. This assumption is motivated by quantum phase estimation (QPE) and digital adiabatic simulation (DAS). Treating the effective Hamiltonian that generates the Trotterized time evolution using rigorous perturbative methods, we show that the Trotter step size needed to estimate an energy eigenvalue within precision $ε$ using QPE can be improved in scaling from $ε$ to $ε^…
Joint Center for Quantum Information and Computer Science, NIST/University of Maryland(量子信息与计算联合中心,美国国家标准与技术研究院/马里兰大学);Department of Computer Science, University of Maryland(马里兰大学计算机科学系);Joint Quantum Institute, NIST/University of Maryland(量子信息联合研究所,美国国家标准与技术研究院/马里兰大学);Quantinuum;Institute for Advanced Computer Studies, University of Maryland(马里兰大学高级计算机研究所)
We present a product formula to approximate the exponential of a skew-Hermitian operator that is a sum of generators of a Lie algebra. The number of terms in the product depends on the structure factors. When the generators have large norm with respect to the dimension of the Lie algebra, or when the norm of the effective operator resulting from nested commutators is less than the product of the norms, the number of terms in the product is significantly less than that obtained from well-known results. We apply our results to construct product formulas useful for the quantum simulation of some …
Joint Mitigation of Algorithmic and Physical Errors in Noisy Hamiltonian Simulation
Center on Frontiers of Computing Studies, Peking University(北京大学前沿计算研究中心);School of Computer Science, Peking University(北京大学计算机学院);Tencent Quantum Laboratory, Tencent(腾讯量子实验室);Department of Mathematical Sciences, Tsinghua University(清华大学数学科学系);Yau Mathematical Sciences Center, Tsinghua University(清华大学丘成桐数学科学中心);RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)(理化学研究所跨学科理论数学科学中心);RIKEN Center for Computational Science (R-CCS)(理化学研究所计算科学中心)
Trotter error compensation with polylogarithmic precision and nested-commutator scaling without ancillas
Center on Frontiers of Computing Studies, Peking University(前沿计算研究中心,北京大学);School of Computer Science, Peking University(计算机学院,北京大学);Institute of Natural Sciences, Shanghai Jiao Tong University(自然科学研究院,上海交通大学);School of Physics and Astronomy, Shanghai Jiao Tong University(物理与天文学院,上海交通大学);School of Physical and Chemical Sciences, Queen Mary University of London(物理与化学科学学院,伦敦大学玛丽女王学院)
The book deals with a stochastic formulation of path integration in real time, by rotating the_space_ variables over exp(i pi/4). Preliminary chapters deal with quantum and classical mechanics, probability theory and stochastic calculus, and the conventional approach to path integration through the Trotter product formula. Subsequently, the stochastic formulation in complex space is established, and applied to semi-classical expansions, nonlinear oscillations, quantum dynamics on analytic manifolds, dissipative systems (i.e., those which are open in that they interact with an environment), tun…
The Lie-Trotter formula, together with its higher-order generalizations, provides a direct approach to decomposing the exponential of a sum of operators. Despite significant effort, the error scaling of such product formulas remains poorly understood. We develop a theory of Trotter error that overcomes the limitations of prior approaches based on truncating the Baker-Campbell-Hausdorff expansion. Our analysis directly exploits the commutativity of operator summands, producing tighter error bounds for both real- and imaginary-time evolutions. Whereas previous work achieves similar goals for sys…
Center for Quantum Information and Control, University of New Mexico(新墨西哥大学量子信息与控制中心);Quantum and Condensed Matter Physics Group (T-4), Theoretical Division, Los Alamos National Laboratory(洛斯阿拉莫斯国家实验室理论部量子与凝聚态物理组(T-4))
We present a decomposition scheme based on Lie-Trotter-Suzuki product formulae to represent an ordered operator exponential as a product of ordinary operator exponentials. We provide a rigorous proof that does not use a time-displacement superoperator, and can be applied to non-analytic functions. Our proof provides explicit bounds on the error and includes cases where the functions are not infinitely differentiable. We show that Lie-Trotter-Suzuki product formulae can still be used for functions that are not infinitely differentiable, but that arbitrary order scaling may not be achieved.
A generalized Feynman-Kac formula based on the Wiener measure is presented. Within the setting of a quantum particle in an electromagnetic field it yields the standard Feynman-Kac formula for the corresponding Schrödinger semigroup. In this case rigorous criteria for its validity are compiled. Finally, phase-space path-integral representations for more general quantum Hamiltonians are derived. These representations rely on a generalized Lie-Trotter formula which takes care of the operator-ordering multiplicity, but in general is not related to a path measure.
Product formula approximations of the time-evolution operator on quantum computers are of great interest due to their simplicity, and good scaling with system size by exploiting commutativity between Hamiltonian terms. However, product formulas exhibit poor scaling with the time $t$ and error $ε$ of simulation as the gate cost of a single step scales exponentially with the order $m$ of accuracy. We introduce well-conditioned multiproduct formulas, which are a linear combination of product formulas, where a single step has polynomial cost $\mathcal{O}(m^2\log{(m)})$ and succeeds with probabilit…
We propose a modification of the Faddeev-Popov procedure to construct a path integral representation for the transition amplitude and the partition function for gauge theories whose orbit space has a non-Euclidean geometry. Our approach is based on the Kato-Trotter product formula modified appropriately to incorporate the gauge invariance condition, and thereby equivalence to the Dirac operator formalism is guaranteed by construction. The modified path integral provides a solution to the Gribov obstruction as well as to the operator ordering problem when the orbit space has curvature. A few ex…
In this short communication I generalize the method of obtaining quasi-Feynman formulas described in my previous paper on that topic. The theorem presented allows to obtain the solution to the Cauchy problem for the Schrödinger equation with the Hamiltonian decomposed to a finite sum of operators. The concept of Chernoff tangency is used, and the solution is written in the form of a quasi-Feynman formula as before. Theorem proven is compared to known approximation theorems: Trotter's, Chernoff's, Butko-Schilling-Smolyanov's.
The cavity method is a well established technique for solving classical spin models on sparse random graphs (mean-field models with finite connectivity). Laumann et al. [arXiv:0706.4391] proposed recently an extension of this method to quantum spin-1/2 models in a transverse field, using a discretized Suzuki-Trotter imaginary time formalism. Here we show how to take analytically the continuous imaginary time limit. Our main technical contribution is an explicit procedure to generate the spin trajectories in a path integral representation of the imaginary time dynamics. As a side result we also…
Multi-Product Hamiltonian Simulation with Explicit Commutator Scaling
University of Maryland, College Park(马里兰大学帕克分校);Joint Center for Quantum Information and Computer Science, University of Maryland, College Park(马里兰大学帕克分校量子信息与计算机科学联合中心);Institute for Physical Science and Technology, University of Maryland, College Park(马里兰大学帕克分校物理科学与技术研究所)
In the present article, we review a continual effort on generalization of the Trotter formula to higher-order exponential product formulas. The exponential product formula is a good and useful approximant, particularly because it conserves important symmetries of the system dynamics. We focuse on two algorithms of constructing higher-order exponential product formulas. The first is the fractal decomposition, where we construct higher-order formulas recursively. The second is to make use of the quantum analysis, where we compute higher-order correction terms directly. As interludes, we also hav…
Fully analytic formulas, which do not involve any numerical integration, are derived for the discretized influence functionals of a very extensive assortment of spectral distributions. For Feynman integrals derived using the Trotter splitting and Strang splitting, we present general formulas for the discretized influence functionals in terms of proper integrals of the bath response function. When an analytic expression exists for the bath response function, these integrals can almost always be evaluated analytically. In cases where these proper integrals cannot be integrated analytically, nume…