scholarly journals Exponentially faster implementations of Select(H) for fermionic Hamiltonians

Quantum ◽  
2021 ◽  
Vol 5 ◽  
pp. 380
Author(s):  
Kianna Wan
Keyword(s):  
Quantum Chemistry ◽  
General Framework ◽  
State Of The Art ◽  
Quantum Algorithms ◽  
Condensed Matter ◽  
Quantum Circuits ◽  
Constant Independent ◽  
Wigner Transform ◽  
Gate Count ◽  
Hamiltonian Simulation

We present a simple but general framework for constructing quantum circuits that implement the multiply-controlled unitary Select(H):=∑ℓ|ℓ⟩⟨ℓ|⊗Hℓ, where H=∑ℓHℓ is the Jordan-Wigner transform of an arbitrary second-quantised fermionic Hamiltonian. Select(H) is one of the main subroutines of several quantum algorithms, including state-of-the-art techniques for Hamiltonian simulation. If each term in the second-quantised Hamiltonian involves at most k spin-orbitals and k is a constant independent of the total number of spin-orbitals n (as is the case for the majority of quantum chemistry and condensed matter models considered in the literature, for which k is typically 2 or 4), our implementation of Select(H) requires no ancilla qubits and uses O(n) Clifford+T gates, with the Clifford gates applied in O(log2n) layers and the T gates in O(logn) layers. This achieves an exponential improvement in both Clifford- and T-depth over previous work, while maintaining linear gate count and reducing the number of ancillae to zero.

scholarly journals Algorithmic Error Mitigation Scheme for Current Quantum Processors

Quantum ◽  
2021 ◽  
Vol 5 ◽  
pp. 492
Author(s):  
Philippe Suchsland ◽  
Francesco Tacchino ◽  
Mark H. Fischer ◽  
Titus Neupert ◽  
Panagiotis Kl. Barkoutsos ◽  
...  
Keyword(s):  
Quantum Chemistry ◽  
Ground State ◽  
State Of The Art ◽  
Quantum Algorithms ◽  
Quantum Circuit ◽  
Lanczos Method ◽  
Error Mitigation ◽  
Near Term ◽  
The Impact ◽  
Different Sources

We present a hardware agnostic error mitigation algorithm for near term quantum processors inspired by the classical Lanczos method. This technique can reduce the impact of different sources of noise at the sole cost of an increase in the number of measurements to be performed on the target quantum circuit, without additional experimental overhead. We demonstrate through numerical simulations and experiments on IBM Quantum hardware that the proposed scheme significantly increases the accuracy of cost functions evaluations within the framework of variational quantum algorithms, thus leading to improved ground-state calculations for quantum chemistry and physics problems beyond state-of-the-art results.

scholarly journals Circuit optimization of Hamiltonian simulation by simultaneous diagonalization of Pauli clusters

Quantum ◽  
2020 ◽  
Vol 4 ◽  
pp. 322
Author(s):  
Ewout van den Berg ◽  
Kristan Temme
Keyword(s):  
Quantum Chemistry ◽  
Time Evolution ◽  
Circuit Complexity ◽  
Practical Interest ◽  
Quantum Circuits ◽  
Circuit Optimization ◽  
Simultaneous Diagonalization ◽  
Hamiltonian Simulation ◽  
Practical Algorithm ◽  
Circuit Depth

Many applications of practical interest rely on time evolution of Hamiltonians that are given by a sum of Pauli operators. Quantum circuits for exact time evolution of single Pauli operators are well known, and can be extended trivially to sums of commuting Paulis by concatenating the circuits of individual terms. In this paper we reduce the circuit complexity of Hamiltonian simulation by partitioning the Pauli operators into mutually commuting clusters and exponentiating the elements within each cluster after applying simultaneous diagonalization. We provide a practical algorithm for partitioning sets of Paulis into commuting subsets, and show that the proposed approach can help to significantly reduce both the number of CNOT operations and circuit depth for Hamiltonians arising in quantum chemistry. The algorithms for simultaneous diagonalization are also applicable in the context of stabilizer states; in particular we provide novel four- and five-stage representations, each containing only a single stage of conditional gates.

Thermodynamics and Control of Open Quantum Systems

2021 ◽  
Author(s):  
Gershon Kurizki ◽  
Abraham G. Kofman
Keyword(s):  
Quantum Chemistry ◽  
Quantum Physics ◽  
Open Quantum Systems ◽  
Condensed Matter ◽  
Quantum Systems ◽  
Open Quantum ◽  
Heat Engines ◽  
Chemistry Research ◽  
And Control ◽  
Quantum Thermodynamic

The control of open quantum systems and their associated quantum thermodynamic properties is a topic of growing importance in modern quantum physics and quantum chemistry research. This unique and self-contained book presents a unifying perspective of such open quantum systems, first describing the fundamental theory behind these formidably complex systems, before introducing the models and techniques that are employed to control their quantum thermodynamics processes. A detailed discussion of real quantum devices is also covered, including quantum heat engines and quantum refrigerators. The theory of open quantum systems is developed pedagogically, from first principles, and the book is accessible to graduate students and researchers working in atomic physics, quantum information, condensed matter physics, and quantum chemistry.

scholarly journals Fast equivalence -- checking for quantum circuits

2010 ◽  
Vol 10 (9&10) ◽  
pp. 721-734
Author(s):  
Shigeru Yamashita ◽  
Igor L. Markov
Keyword(s):  
Formal Verification ◽  
Quantum Algorithms ◽  
Quantum Circuits ◽  
Equivalence Checking ◽  
Sat Solvers ◽  
Reversible Circuits ◽  
Verification Tools ◽  
Verification Methodology ◽  
Verification Techniques ◽  
Factoring Algorithm

We perform formal verification of quantum circuits by integrating several techniques specialized to particular classes of circuits. Our verification methodology is based on the new notion of a reversible miter that allows one to leverage existing techniques for simplification of quantum circuits. For reversible circuits which arise as runtime bottlenecks of key quantum algorithms, we develop several verification techniques and empirically compare them. We also combine existing quantum verification tools with the use of SAT-solvers. Experiments with circuits for Shor's number-factoring algorithm, containing thousands of gates, show improvements in efficiency by four orders of magnitude.

scholarly journals Comparison of Two Efficient Methods for Calculating Partition Functions

Entropy ◽  
2019 ◽  
Vol 21 (11) ◽  
pp. 1050 ◽  
Author(s):  
Le-Cheng Gong ◽  
Bo-Yuan Ning ◽  
Tsu-Chien Weng ◽  
Xi-Jing Ning
Keyword(s):  
Sampling Method ◽  
State Of The Art ◽  
Condensed Matter ◽  
Dynamics Simulation ◽  
Integral Approach ◽  
Partition Functions ◽  
Direct Integral ◽  
Nested Sampling ◽  
Long Time ◽  
Solid Argon

In the long-time pursuit of the solution to calculating the partition function (or free energy) of condensed matter, Monte-Carlo-based nested sampling should be the state-of-the-art method, and very recently, we established a direct integral approach that works at least four orders faster. In present work, the above two methods were applied to solid argon at temperatures up to 300 K. The derived internal energy and pressure were compared with the molecular dynamics simulation as well as experimental measurements, showing that the calculation precision of our approach is about 10 times higher than that of the nested sampling method.

scholarly journals An Innovative Genetic Algorithm for the Quantum Circuit Compilation Problem

2019 ◽  
Vol 33 ◽  
pp. 7707-7714
Author(s):  
Riccardo Rasconi ◽  
Angelo Oddi
Keyword(s):  
Genetic Algorithm ◽  
Nearest Neighbor ◽  
Quantum Algorithms ◽  
Quantum Circuit ◽  
Quantum Circuits ◽  
Heuristic Function ◽  
Circuit Realization ◽  
Benchmark Instances ◽  
Technological Limitations ◽  
Selection Of

Quantum Computing represents the next big step towards speed boost in computation, which promises major breakthroughs in several disciplines including Artificial Intelligence. This paper investigates the performance of a genetic algorithm to optimize the realization (compilation) of nearest-neighbor compliant quantum circuits. Currrent technological limitations (e.g., decoherence effect) impose that the overall duration (makespan) of the quantum circuit realization be minimized, and therefore the makespanminimization problem of compiling quantum algorithms on present or future quantum machines is dragging increasing attention in the AI community. In our genetic algorithm, a solution is built utilizing a novel chromosome encoding where each gene controls the iterative selection of a quantum gate to be inserted in the solution, over a lexicographic double-key ranking returned by a heuristic function recently published in the literature.Our algorithm has been tested on a set of quantum circuit benchmark instances of increasing sizes available from the recent literature. We demonstrate that our genetic approach obtains very encouraging results that outperform the solutions obtained in previous research against the same benchmark, succeeding in significantly improving the makespan values for a great number of instances.

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