Non-collapsing electric readout of arbitrary Andreev qubits

Abstract: Nondemolition protocols use ancilla qubits to identify the fragile quantum state of a qubit without destroying its encoded information, thus playing a crucial role in nondestructive quantum measurements particularly relevant for quantum error correction. However, the multitude of ancilla preparations, information transfers, and ancilla measurements in these protocols create an intrinsic overhead for information processing. Here we consider an Andreev qubit defined in a quantum-dot Josephson junction and show that the intrinsic time-dependent oscillatory supercurrent arising from the quantum interference of the many-body eigenstates of the Andreev qubit, can be used to probe the qubit itself nondestructively and \textit{without} collapsing its quantum state. This nondestructive and non-collapsing readout of arbitrary superposition states of Andreev qubits avoids ancilla qubits altogether and significantly reduces experimental overhead as no repetitive qubit resetting is needed. Our findings should have an unprecedented impact on advancing research and applications involving Andreev dots, thus positioning them as promising qubit contenders for quantum processing and technologies.