Multi-qubit gates and 'Schrödinger cat' states in an optical clock
arxiv(2024)
摘要
Many-particle entanglement is a key resource for achieving the fundamental
precision limits of a quantum sensor. Optical atomic clocks, the current
state-of-the-art in frequency precision, are a rapidly emerging area of focus
for entanglement-enhanced metrology. Augmenting tweezer-based clocks featuring
microscopic control and detection with the high-fidelity entangling gates
developed for atom-array information processing offers a promising route
towards leveraging highly entangled quantum states for improved optical clocks.
Here we develop and employ a family of multi-qubit Rydberg gates to generate
'Schrödinger cat' states of the Greenberger-Horne-Zeilinger (GHZ) type with
up to 9 optical clock qubits in a programmable atom array. In an atom-laser
comparison at sufficiently short dark times, we demonstrate a fractional
frequency instability below the standard quantum limit using GHZ states of up
to 4 qubits. A key challenge to improving the optimal achievable clock
precision with GHZ states is their reduced dynamic range. Towards overcoming
this hurdle, we simultaneously prepare a cascade of varying-size GHZ states to
perform unambiguous phase estimation over an extended interval. These results
demonstrate key building blocks for approaching Heisenberg-limited scaling of
optical atomic clock precision.
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