Hexagonal Boron Nitride Quantum Simulator: Prelude to Spin and Photonic Qubits

Abstract

The quest for qubit operation at room temperature is accelerating the field of quantum information science and technology. Solid state quantum defects with spin-optical properties are promising spin- and photonic qubit candidates for room temperature operations. In this regard, a single boron vacancy within hexagonal boron nitride (h-BN) lattice such as V_B^- defect has coherent quantum interfaces for spin and photonic qubits owing to the large band gap of h-BN (6 eV) that can shield a computational subspace from environmental noise. However, for a V_B^- defect in h-BN to be a potential quantum simulator, the design and characterization of the Hamiltonian involving mutual interactions of the defect and other degrees of freedom are needed to fully understand the effect of defects on the computational subspace. Here, we studied the key coupling tensors such as zero-field splitting, Zeeman effect, and hyperfine splitting in order to build the Hamiltonian of the V_B^- defect. These eigenstates are spin triplet states that form a computational subspace. To study the phonon-assisted single photon emission in the V_B^- defect, the Hamiltonian is characterized by electron-phonon interaction with Jahn-Teller distortions. A theoretical demonstration of how the V_B^- Hamiltonian is utilized to relate these quantum properties to spin- and photonic-quantum information processing. For selecting promising host 2D materials for spin and photonic qubits, we present a data-mining perspective based on the proposed Hamiltonian engineering of the V_B^- defect in which h-BN is one of four materials chosen to be room temperature qubit candidates.

Keywords: hexagonal boron nitride; quantum defect; quantum information science; quantum simulator; qubit; single photon emission.

Figure 1

Abstract workflow for the realization of solid-state defect qubit in an atomically thin material. Starting with an ab initio understanding of critical properties and behaviors of quantum defect in h-BN, we then study the Hamiltonian that fully describes the defect’s spin states. Finally, we present a model that maps the spin-states to a computational framework that can be utilized for quantum computing and quantum sensing (ℏ = 1).

Figure 2

Spin-optical properties of V_B^– quantum defect. (a) The h-BN lattice with a V_B^– defect. (b) Schematic for single-photon emission through an excited defect state induced by an excitation. (c) Comparison of various charge states of boron vacancy defect such as V_B⁰, V_B^–, and V_B^2– at room temperature. Density functional theory analysis demonstrates stability of negatively changed spin-1 V_B^– defect state, whereas the spin-3/2 V_B⁰, and V_B^2– states are not energetically stable at room temperature. The charge state V_B^3– is entirely improbable and therefore, the charge state is not shown.

Figure 3

Spin-optical properties of V_B^– h-BN defect. (a) Zero-field splitting energy spectrum of ground (green) and excited (red) state with a spin-0 metastable state (blue). The zero-field parameters for ground- (D_GS and E_GS), and excited- (D_ES and E_ES) states are shown. (b) Zeeman effect of ground spin states induce energy splitting for m_s = ± 1 states. (c) Phonon modes enable a harmonic basis that influences the computational state of the qubit. The V_B^– defect-phonon coupling, g, leads to a Jaynes-Cumming-like energy structure.

Figure 4

Most promising host materials for spin-qubits in C2DB: (a) h-BN; (b) K₂C₂H₂O₆; (c) Na₂H₂O₂; (d) Li₂H₂O₂. Element colors: B: green; N: off-white; K: purple; O: red; C: brown; Yellow: Na; Light green: Li.