Quantum Computation SG Seminar
3 events

Seminar
Quantum Computation Study Group Seminars
June 18 (Tue) at 13:30  15:00, 2024
Yuta Kikuchi (Research Scientist, Quantum algorithms and machine learning, Quantinuum K.K.)
Ermal Rrapaj (HPC Architecture and Performance Engineer, National Energy Research Scientific Computing Center (NERSC), Lawrence Berkeley National Laboratory (LBNL), USA)Speaker: Yuta Kikuchi Title: Simulating Floquet scrambling circuits on trappedion quantum computers Abstract: Complex quantum manybody dynamics spread initially localized quantum information across the entire system. Information scrambling refers to such a process, whose simulation is one of the promising applications of quantum computing. We demonstrate the HaydenPreskill recovery protocol and the interferometric protocol for calculating outoftimeordered correlators to study the scrambling property of a onedimensional kickedIsing model on 20qubit trappedion quantum processors. The simulated quantum circuits have a geometrically local structure that exhibits the ballistic growth of entanglement, resulting in the circuit depth being linear in the number of qubits for the entire state to be scrambled. We experimentally confirm the growth of signals in the HaydenPreskill recovery protocol and the decay of outoftimeordered correlators at late times. As an application of the created scrambling circuits, we also experimentally demonstrate the calculation of the microcanonical expectation values of local operators adopting the idea of thermal pure quantum states. Speaker: Ermal Rrapaj Title: Exact block encoding of imaginary time evolution with universal quantum neural networks Abstract: Quantum computers have been widely speculated to offer significant advantages in obtaining the ground state of difficult Hamiltonian in chemistry and physics. The imaginarytime evolution method is a wellknown approach used for obtaining the ground state in quantum manybody problems on a classical computer. In this work we develop a practical method for such purpose. We develop a constructive approach to generate quantum neural networks capable of representing the exact thermal states of all manybody qubit Hamiltonians. The Trotter expansion of the imaginarytime propagator is implemented through an exact block encoding by means of a unitary, restricted Boltzmann machine architecture. Marginalization over the hiddenlayer neurons (auxiliary qubits) creates the nonunitary action on the visible layer. Then, we introduce a unitary deep Boltzmann machine architecture, in which the hiddenlayer qubits are allowed to couple laterally to other hidden qubits. We prove that this wave function ansatz is closed under the action of the imaginarytime propagator and, more generally, can represent the action of a universal set of quantum gate operations. We provide analytic expressions for the coefficients for both architectures, thus enabling exact network representations of thermal states without stochastic optimization of the network parameters. In the limit of large imaginary time, the ansatz yields the ground state of the system. The number of qubits grows linearly with the system size and total imaginary time for a fixed interaction order. Both networks can be readily implemented on quantum hardware via midcircuit measurements of auxiliary qubits. If only one auxiliary qubit is measured and reset, the circuit depth scales linearly with imaginary time and system size, while the width is constant. Alternatively, one can employ a number of auxiliary qubits linearly proportional to the system size, and circuit depth grows linearly with imaginary time only.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English

Using a trapped ion quantum computer for hamiltonian simulations
February 28 (Wed) at 10:30  12:00, 2024
Enrico Rinaldi (Senior Research Scientist, Quantum Machine Learning and Algorithms, Quantinuum K.K.)
Trapped ion quantum computers, like the Hseries quantum hardware by Quantinuum, robustly encode quantum information in long lived and precise qubits. However, utilizing the hardware efficiently requires a fullstack workflow from software libraries to hardware compilers. In this talk we introduce the relevant elements of this stack in the context of solving the quantum dynamics of a spin system on Hseries hardware: we start from the definition of the Hamiltonian operator in the qubit Hilbert space using the opensource pytket python library and we define the quantum circuits in measurements to run, on a simulator first and on hardware later.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Energy spectrum and time evolution of a SU(2) pure gauge lattice theory on a quantum annealer
December 18 (Mon) at 14:00  15:00, 2023
Emanuele Mendicelli (Postdoctoral Research Associate, Department of Mathematical Sciences, University of Liverpool, UK)
Lattice gauge theory is an indispensable tool for nonAbelian fields, such as those in quantum chromodynamics where lattice results have been of central importance for several decades. Recent studies suggest that quantum hardware could extend the reach of lattice gauge theory to inaccessible phenomena due to the need for an exponentially large amount of resources, the socalled sign problem. Among the available quantum hardware gatebased quantum computer are well know but less common quantum annealer can play a role too. In this talk we briefly report one of the first use of DWave quantum annealer to study the energy spectrum and the time evolution of a SU(2) pure gauge lattice theory in its Hamiltonian formulation. In particular we present how to extract the energy spectrum using the quantum Quantum Annealer Eigensolver algorithm and perform the time evolution using the KitaevFeynman clock states. Despite the nosy hardware, no error mitigation techniques were needed but the usability of the DWave hardware was extended by simply blockdiagonalizing the Hamiltonian.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
3 events