A quantum bus is a device which can be used to store or transfer information between independent qubits in a quantum computer, or combine two qubits into a superposition. It is the quantum analog of a classical bus.
There are several physical systems that can be used to realize a quantum bus, including trapped ions, photons, and superconducting qubits. Trapped ions, for example, can use the quantized motion of ions (phonons) as a quantum bus, while photons can act as a carrier of quantum information by utilizing the increased interaction strength provided by cavity quantum electrodynamics. Circuit quantum electrodynamics, which uses superconducting qubits coupled to a microwave cavity on a chip, is another example of a quantum bus that has been successfully demonstrated in experiments.
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
\hat{H}=\hat{H}r+\sum\limitsj=A,B\hat{H}j+\sum\limitsj=A,B
| \dagger\hat{\sigma} | |
| hg | |
| i\left(\hat{a} |
| j | |
| + |
\right)
\hat{H}j=
| 1 | |
| 2 |
| j | |
| \hbar\omega | |
| - |
| j | |
| \hat{\sigma} | |
| - |
j
\hbar\omegaj