Abstract: A system and method provide two-qubit gates and quantum computing circuits built therefrom. Pairs of qubits are inductively or capacitively coupled using a coupler that is driven using an off-resonant microwave drive. By controlling the drive, the ZZ interaction between the qubits can be precisely controlled. In particular, the interaction may be selectively reduced or suppressed, thereby isolating the qubits from each other, or the interaction may be increased to provide fast, controlled-Z, two-qubit gates with high fidelity. Moreover, qubits and couplers may be arranged according to their resonant frequencies into unit cells and replicated to arbitrary size, thereby forming a quantum computer.

Abstract: Disclosed herein are methods, systems, and devices including a tunable coupler design that harnesses interference due to higher energy levels to achieve zero static ZZ coupling between the two qubits. Biasing to zero ZZ interaction, a fast perfect entangler is realized with parametric flux modulation in less than 20 ns. The disclosed coupler provides very fast gates between far-detuned fixed frequency qubits, and is a crucial building block in scaled quantum computers.

Abstract: The generally quantum system can have : a first quantum subsystem having a first set of eigenstates; a second quantum subsystem having a second set of eigenstates; a coupler connected to both the first quantum system and to the second quantum system, the coupler having a third set of eigenstates; at least one interaction drive configured to control interaction between the first set of eigenstates and the second set of eigenstates via transitions within the third set of eigenstates; an auxiliary quantum subsystem connected to the coupler; and an attenuation drive selectively operable at a drive amplitude to generate a set of stabilized states in the auxiliary quantum system, said set of stabilized states being entangled with the third set of eigenstates in a manner that the probability of said transition within the third set of eigenstates is set by a probability of transition in the set of stabilized states.

Abstract: A quantum circuit called a “qumon” is provided to cancel unwanted ZZ interaction in a superconducting qubit architecture. The qumon qubit has a high coherence, and a positive anharmonicity that may be tuned to cancel the negative anharmonicity in a coupled qubit, such as a transmon qubit. The qumon has three parallel branches, in which are a shunt capacitor; a Josephson junction having weighted energy level and capacitance; and several Josephson junctions in series. The weight is chosen to provide the desired anharmonicity, and the transverse flux noise and transverse charge noise each decrease in proportion to the number of the Josephson junctions in series. Because unwanted ZZ interactions are canceled, qumon qubits and transmon qubits may be capacitively coupled in an alternating pattern to provide a surface code in which these interactions are canceled in an extensible way.

Abstract: A quantum circuit called a “qumon” is provided to cancel unwanted ZZ interaction in a superconducting qubit architecture. The qumon qubit has a high coherence, and a positive anharmonicity that may be tuned to cancel the negative anharmonicity in a coupled qubit, such as a transmon qubit. The qumon has three parallel branches, in which are a shunt capacitor; a Josephson junction having weighted energy level and capacitance; and several Josephson junctions in series. The weight is chosen to provide the desired anharmonicity, and the transverse flux noise and transverse charge noise each decrease in proportion to the number of the Josephson junctions in series. Because unwanted ZZ interactions are canceled, qumon qubits and transmon qubits may be capacitively coupled in an alternating pattern to provide a surface code in which these interactions are canceled in an extensible way.