  The quantum mechanics of Schwarzschild-de Sitter black holes is of great
recent interest because of their peculiar thermodynamic properties as well as
their realization in modern dark energy cosmology which indicates the presence
of a small positive cosmological constant. We study Schwarzschild-de Sitter
black holes and also the Kantowki-Sachs Cosmology using quantum computing. In
these cases in addition to the Hamiltonian there is a Mass operator which plays
an important role in describing the quantum states of the black hole and
Kantowski-Sachs cosmology. We compute the spectrum of these operators using
classical and quantum computing. For quantum computing we use the Variational
Quantum Eigensolver which is hybrid classical-quantum algorithm that runs on
near term quantum hardware. We perform our calculations using 4, 6 and 8 qubits
in a harmonic oscillator basis, realizing the quantum operators of the
Schwarzschild-de Sitter black hole and Kantowski-Sachs cosmology in terms of 16
x 16, 64 x 64 and 256 x 256 matrices respectively. For the 4 qubit case we find
highly accurate results but for the other cases we find a more refined
variational ansatz will be necessary to represent the quantum states of a
Schwarzschild-de Sitter black hole or Kantowki-Sachs cosmology accurately on a
quantum computer.
