Resonant controlled qubit system
View Patent ↗A circuit comprising a superconducting qubit and a resonant control system that is characterized by a resonant frequency. The resonant frequency of the control system is a function of a bias current. The circuit further includes a superconducting mechanism having a capacitance or inductance. The superconducting mechanism coherently couples the superconducting qubit to the resonant control system. A method for entangling a quantum state of a first qubit with the quantum state of a second qubit. In the method, a resonant control system, which is capacitively coupled to the first and second qubit, is tuned to a first frequency that corresponds to the energy differential between the lowest two potential energy levels of the first qubit. The resonant control system is then adjusted to a second frequency corresponding to energy differential between the lowest two potential energy levels of the second qubit.
1. A method for entangling a quantum state of a first qubit with a quantum state of a second qubit, the method comprising:
(A) tuning a ground state energy difference between a potential energy state of said first qubit and a potential energy state of said second qubit so that the energy difference corresponds to a predetermined frequency; and
(B) biasing a resonant control system, which is capacitively coupled to said first qubit and second qubit, to said predetermined frequency for a period of time.
2. The method of claim 1 , wherein said resonant control system comprises a Josephson junction and a bias current source that is connected in series with the Josephson junction, and wherein said biasing comprises adjusting said bias current source.
3. The method of claim 2 , wherein said bias current source is 0.994*I c or less during said biasing, where I c is the critical current value of the Josephson junction in the resonant control system.
4. The method of claim 2 , wherein said bias current source is 0.990*I c or less during said biasing, where I c is the critical current value of the Josephson junction in the resonant control system.
5. The method of claim 1 , the method further comprising:
(C) applying a first quantum gate to said first qubit prior to said tuning in step (A); and
(D) applying a second quantum gate to said first qubit after said tuning in step (A).
6. The method of claim 5 , wherein said first quantum gate is a Hadamard gate and said second quantum gate is a Hadamard gate.
7. The method of claim 1 , the method further comprising:
(C) applying a first quantum gate to said second qubit prior to said biasing in step (B); and
(D) applying a second quantum gate to said second qubit after said biasing in step (B).
8. The method of claim 7 wherein said first quantum gate is a Hadamard gate and said second quantum gate is a Hadamard gate.
9. The method of claim 1 , wherein said first qubit, said second qubit, or both said first and second qubits are described by a native interaction Hamiltonian that comprises an off diagonal interaction term.
10. The method of claim 9 , wherein said first qubit, said second qubit, or both said first qubit and said second qubit are a superconducting charge qubit.
11. The method of claim 1 , wherein said first qubit, said second qubit, or both said first qubit and said second qubit are described by a native interaction Hamiltonian that comprises a diagonal interaction term.
12. The method of claim 11 , wherein said first qubit, said second qubit, or both said first qubit and said second qubit is a charge qubit, a phase qubit, or a flux qubit.