Quantum bus

The concept was first demonstrated by researchers at Yale University and the National Institute of Standards and Technology (NIST) in 2007.[1][2][3] Prior to this experimental demonstration, the quantum bus had been described by scientists at NIST as one of the possible cornerstone building blocks in quantum computing architectures.[4][5]

A quantum bus for superconducting qubits can be built with a resonance cavity. The hamiltonian for a system with qubit A, qubit B, and the resonance cavity or quantum bus connecting the two is ${\displaystyle {\hat {H}}={\hat {H}}_{r}+\sum \limits _{j=A,B}{\hat {H}}_{j}+\sum \limits _{j=A,B}hg_{i}\left({\hat {a}}^{\dagger }{\hat {\sigma }}_{-}^{j}+{\hat {a}}{\hat {\sigma }}_{\text{+}}^{j}\right)}$ where ${\displaystyle {\hat {H}}_{j}={\frac {1}{2}}\hbar \omega _{j}{\hat {\sigma }}_{+}^{j}{\hat {\sigma }}_{-}^{j}}$ is the single qubit hamiltonian, ${\displaystyle {\hat {\sigma }}_{+}^{j}{\hat {\sigma }}_{-}^{j}}$ is the raising or lowering operator for creating or destroying excitations in the ${\displaystyle j}$th qubit, and ${\displaystyle \hbar \omega _{j}}$ is controlled by the amplitude of the D.C. and radio frequency flux bias.[6]