Preserving a Qubit During Adjacent Measurements at a Few Micrometers Distance
Abstract:
Protecting a quantum object against irreversible accidental measurements from its surroundings is necessary for controlled quantum operations. This becomes especially challenging or unfeasible if one must simultaneously measure or reset a nearby object's quantum state, such as in quantum error correction.
In atomic systems - among the most established quantum information processing platforms - current attempts to preserve qubits against resonant laser-driven adjacent measurements, waste valuable experimental resources such as coherence time or extra qubits and introduce additional errors. We preserve the quantum state of an 'asset' ion qubit with high fidelity, while a neighbouring qubit at a few microns distance is reset/measured. We achieve < 1 x 10-3 probability of accidental measurement of the asset qubit during a neighbouring qubit reset and < 4 x 10-3 while applying a detection beam on the same neighbour, for 11 μs, at a distance of 6 μm or 4 times the addressing Gaussian beam waist (permitted by the numerical aperture).
These low probabilities correspond to the preservation of the quantum state of the qubit with fidelities above 99.90% (state-reset) and 99.6% (state-measurement). Our results are enabled by precise wavefront control of the addressing optical beams, while utilizing a single ion as a quantum sensor of optical aberrations.
Our work demonstrates the feasibility of in-situ state-reset and measurement operations, building towards enhancements in the speed and capabilities of quantum processors such as in simulating measurement-driven quantum phases and realizing quantum error correction.
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