Quantum error-correction in microwave integrated quantum circuits
In some implementations, a quantum error-correction technique includes applying a first set of two-qubit gates to qubits in a lattice cell, and applying a second, different set of two-qubit gates to the qubits in the lattice cell. The qubits in the lattice cell include data qubits and ancilla qubits, and the ancilla qubits reside between respective nearest-neighbor pairs of the data qubits. After the first and second sets of two-qubit gates have been applied, measurement outcomes of the ancilla qubits are obtained, and the parity of the measurement outcomes is determined.
1 . A method to perform quantum error-correction in a quantum computing system, the quantum computing system comprising a quantum processor cell comprising a device lattice, the device lattice comprising an array of lattice cells, each lattice cell comprising transmon devices defining data qubits and tunable coupler devices defining ancilla qubits, the method comprising:
identifying a two-qubit quantum logic gate to be applied to a first data qubit of the data qubits and a first ancilla qubit of the ancilla qubits;
generating, by operation of a control system associated with the quantum processor cell, a control sequence configured to apply the two-qubit quantum logic gate to the first data qubit and the first ancilla qubit, the control sequence comprising a control signal, the two-qubit quantum logic gate comprising an iSWAP gate; and
sending the control sequence to the quantum processor cell to execute the two-qubit quantum logic gate.
2 . The method of claim 1 , wherein each of the tunable coupler devices comprises:
a superconducting circuit loop; and
bias circuitry that applies a magnetic bias field to the superconducting circuit loop in response to the control signal.
3 . The method of claim 1 , wherein applying the two-qubit quantum logic gate comprises applying microwave pulses to the device lattice.
4 . The method of claim 1 , wherein the two-qubit quantum logic gate is a first two-qubit quantum logic gate, the control sequence is a first control sequence, the control signal is a first control signal, and the method comprises:
identifying a second two-qubit quantum logic gate to be applied to a second data qubit of the data qubits and a second ancilla qubit of the ancilla qubits;
generating, by operation of the control system, a second control sequence configured to apply the second two-qubit quantum logic gate, the second control sequence comprising a second control signal; and
sending the second control sequence to the quantum processor cell to execute the second two-qubit quantum logic gate.
5 . A quantum computing system comprising:
a quantum processor cell comprising a device lattice, the device lattice comprising an array of lattice cells, each lattice cell comprising transmon devices defining data qubits and tunable coupler devices defining ancilla qubits, and
a control system associated with the quantum processor cell, the control system configured to:
identify a two-qubit quantum logic gate to be applied to a first data qubit of the data qubits and a first ancilla qubit of the ancilla qubits;
generate a control sequence configured to apply the two-qubit quantum logic gate to the first data qubit and the first ancilla qubit, the control sequence comprising a control signal, and the two-qubit quantum logic gate comprising an iSWAP gate; and
send the control sequence to the quantum processor cell to execute the two-qubit quantum logic gate.
6 . The system of claim 5 , wherein each of the tunable coupler devices comprises:
a superconducting circuit loop; and
bias circuitry that applies a magnetic bias field to the superconducting circuit loop in response to the control signal.
7 . The system of claim 5 , wherein applying the two-qubit quantum logic gate comprises applying microwave pulses to the device lattice.
8 . The system of claim 5 , wherein the two-qubit quantum logic gate is a first two-qubit quantum logic gate, the control sequence is a first control sequence, the control signal is a first control signal, and the control system is further configured to:
identify a second two-qubit quantum logic gate to be applied to a second data qubit of the data qubits and a second ancilla qubit of the ancilla qubits;
generate a second control sequence configured to apply the second two-qubit quantum logic gate, the second control sequence comprising a second control signal; and
send the second control sequence to the quantum processor cell to execute the second two-qubit quantum logic gate.