Quantum computing, an approach to deriving information that leverages quantum mechanical effects, relies on qubits, quantum units of information that can exist in superpositions of states. To effectively perform quantum computing, engineers and physicists need to be able to measure the state of qubits efficiently.
In quantum computers based on superconducting materials, qubits are indirectly measured by a so-called readout resonator, a circuit that responds differently based on the state of a qubit. This circuit’s responses are probed using a weak electromagnetic wave, which needs to be amplified to enable its detection.
To amplify these signals, also known as microwave tones, quantum technology engineers rely on devices known as amplifiers. Existing amplifiers, however, have notable limitations. Conventional amplifiers can send unwanted noise back to the qubit, disturbing its state. Superconducting parametric amplifiers introduced more recently can be very efficient, but they conventionally rely on bulky and magnetic hardware components that control the direction of signal and protect qubits from backaction noise.