Quantum-enhanced Hamiltonian simulation offers a promising approach to modeling complex quantum systems, addressing limitations inherent in classical Hamiltonian methods. This paper explores the creation of a novel quantum algorithm to enhance the representation of a Hamiltonian, enabling a more precise and efficient simulation of dynamical behavior. We propose a method that integrates quantum operators directly into the Hamiltonian structure, thereby providing a richer representation of the system's dynamics and potentially unlocking novel insights into complex quantum phenomena. The research focuses on demonstrating the efficacy of this approach through simulations of a specific, yet illustrative, quantum system, highlighting its potential to improve the accuracy and computational efficiency of simulations of intricate quantum systems. The core mechanism involves a layered approach combining existing Hamiltonian techniques with quantum-enhanced representation, leading to a shift in computational capabilities.
Simulating Hamiltonian dynamics is one of the most fundamental and significant tasks for characterizing quantum materials. Recently, a series of quantum algorithms employing block encoding of Hamiltonians have succeeded in providing efficient simulation of time-evolution operators on quantum computers. While time-independent Hamiltonians can be simulated by the quantum eigenvalue transformation (QET) or quantum singular value transformation with the optimal query complexity in time
t and desirable accuracy $\ensuremath{\varepsilon}$, generic time-dependent Hamiltonians face at larger query complexity and more complicated oracles due to the difficulty of handling time-dependency. In this paper, we establish a QET-based approach for simulating time-dependent Hamiltonians with multiple time periodicity. Such time-dependent Hamiltonians involve a variety of nonequilibrium systems such as time-periodic systems (Floquet systems) and time-quasiperiodic systems. Overcoming the difficulty of time dependency, our protocol can simulate the dynamics under multiperiodic time-dependent Hamiltonians with optimal and nearly optimal query complexity both in time
t and desirable accuracy $\ensuremath{\varepsilon}$, and simple oracles as well as the optimal algorithm for time-independent cases.
The computational complexity of simulating the dynamics of physical quantum systems is a central question at the interface of quantum physics and computer science. In this work, we address this question for the simulation of exponentially large bosonic Hamiltonians with quadratic interactions. We present two results: First, we introduce a broad class of quadratic bosonic problems for which we prove that they are BQP-complete. Importantly, this class includes two known BQP-complete problems as special cases: Classical oscillator networks and continuous-time quantum walks. Second, we show that extending the aforementioned class to even more general quadratic Hamiltonians results in a PostBQP-complete problem, which constitutes a jump in the complexity of simulating large quantum systems on a quantum computer, as well as in the difference in complexity between their simulation on classical and quantum computers.