From transistor to trapped-ion computers for quantum chemistry

Abstract

Over the last few decades, quantum chemistry has progressed through the development of computational methods based on modern digital computers. However, these methods can hardly fulfill the exponentially-growing resource requirements when applied to large quantum systems. As pointed out by Feynman, this restriction is intrinsic to all computational models based on classical physics. Recently, the rapid advancement of trapped-ion technologies has opened new possibilities for quantum control and quantum simulations. Here, we present an efficient toolkit that exploits both the internal and motional degrees of freedom of trapped ions for solving problems in quantum chemistry, including molecular electronic structure, molecular dynamics, and vibronic coupling. We focus on applications that go beyond the capacity of classical computers, but may be realizable on state-of-the-art trapped-ion systems. These results allow us to envision a new paradigm of quantum chemistry that shifts from the current transistor to a near-future trapped-ion-based technology.

Exploiting Locality in Quantum Computation for Quantum Chemistry

“…However, it has a significant practical drawback in that after state preparation, all the desired operations must be performed coherently. A different algorithm for energy estimation has recently been introduced [10,13] that lifts all but an O(1) coherence time requirement after state preparation, making it amenable to implementation on quantum devices in the near future. We briefly review this approach, which we will call Hamiltonian averaging, and bound its costs in applications for quantum chemistry.…”

“…As a result, further developments in variational methods [13], quantum cooling [50], and adiabatic state preparation [7,25,51] will be of key importance in this area. Moreover improvements in the ansatze used to prepare the wave function such as multi-configurational self consistent field calculations(MCSCF) [24,25] or unitary coupled cluster (UCC) [10] will be integral parts of any practical quantum computing for quantum chemistry effort.…”

“…showed that these approaches might be particularly promising for quantum chemistry [7]. There have been many developments both in theory [8][9][10] and experimental realization [11][12][13] of quantum chemistry on quantum computers. The original gate construction for quantum chemistry introduced by Whitfield et al [14] was recently challenged as too expensive by Wecker et al [15].…”

Simulation of the elementary evolution operator with the motional states of an ion in an anharmonic trap

“…The coupling with the surroundings is established during the readout process. As predicted by Feynman, 3 quantum computers could be used as quantum simulators to solve stationary [4][5][6][7][8][9] or non stationary 10-13 quantum problems by simulating them with a controllable experimental setup which allows one to reproduce the dynamics of a given Hamiltonian. Several physical supports have been proposed to encode qubits: 14 photons, 15 spin states using nuclear magnetic resonance (NMR) technology, 16 quantum dots, 17 atoms, 18 molecular rovibrational levels of polyatomic or diatomic molecules, ultracold polar molecules, [48][49][50][51][52][53][54][55][56][57] or a juxtaposition of different types of systems.…”

Emulating weak localization using a solid-state quantum circuit

“…As a result, this platform holds great promise for building a large-scale quantum computer 2,3 . These advantages also apply to the construction of quantum simulators [4][5][6][7][8][9][10][11] , for which demonstrations have been made on different problems [12][13][14] . Here, we use a multi-qubit circuit to demonstrate quantum emulation of weak localization, one of the most surprising manifestations of quantum interference in disordered mesoscopic systems.…”