Effective Quantum Simulator for Many 64-qubit Circuits.

Zhaoyun Chen, Qi Zhou, Cheng Xue +3 more

Michael Anshel, Anh Quoc Nguyen

Recently quantum computing has achieved significant results both in theoretical and experimental areas and quantum algorithms have drawn the attention of many scientists. At the present there exist several experiments that realized some parts of certain important quantum algorithms. While those experiments work with only up to seven qubits, quantum simulators allow scientists to design algorithms with many more qubits. The existing simulators have one or more of the following restrictions: either they require powerful computers and additional computation packages such as Matlab or Mathematica or they don't provide an easy method for interacting between the classical and quantum parts of an algorithm. More importantly, none of them can simulate a generic 64-qubit circuit. It is important at this stage of quantum computing development to investigate technological improvements in simulating quantum circuit design. In this thesis we developed a specialized data structure, QSV, for quantum simulators along with new method for calculation of the new state vector after application of a quantum gate in a quantum simulator. We also developed a technique that speeds up the simulation time with our QSV vectors. With those results we built a quantum simulator that overcomes many shortcomings in other simulators and it has many advanced features. Our simulator can simulate many 64-qubit circuits and it can directly simulate multiple qubit gates as well as allows users to define gates with up to 10 qubits. The simulation time is much less in comparison with other simulators we tested. The simulator defines specifications so that users can easily design and test quantum circuits. With the simulator we also developed some new quantum circuits and verified many designs and constructions.

Alice Barthe, Marco Cerezo, Andrew T. Sornborger +2 more

We introduce a framework for simulating, on an (n+1)-qubit quantum computer, the action of a Gaussian bosonic (GB) circuit on a state over 2^{n} modes. Specifically, we encode the initial bosonic state's expectation values over quadrature operators (and their covariance matrix) as an input qubit state. This is then evolved by a quantum circuit that effectively implements the symplectic propagators induced by the GB gates. We find families of GB circuits and initial states leading to efficient quantum simulations. For this purpose, we introduce a dictionary that maps between GB and qubit gates such that particle- (non-particle-) preserving GB gates lead to real- (imaginary-) time evolutions at the qubit level. For the special case of particle-preserving circuits, we present a bounded-error-quantum-polynomial time (BQP)-complete GB decision problem, indicating that GB evolutions of Gaussian states on exponentially many modes are as powerful as universal quantum computers. We also perform numerical simulations of an interferometer on ∼8×10^{9} modes, illustrating the power of our framework.

Md Ahsan Habib

Oleksandr Kyriienko, Anders S. Sørensen

Superconducting circuits are an excellent platform for quantum simulation, with various protocols enacted using highly coherent transmon qubits in a digital (gate-based) approach. Analog simulations with transmons, though, are typically limited by restrictive intercircuit coupling. The authors propose an alternative strategy based on periodic modulation of an effective magnetic field, enabling a Floquet description of the system. This allows one to modify the existing two-qubit interaction and the effective spin Hamiltonian, without modifying the setup. Detailed analysis shows this Floquet-type simulator to be quite advantageous, outperforming state-of-the-art digital approaches.