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The ability to make high-fidelity qubit measurements with minimal collateral disruption to the system is not only relevant to initialization and final read-out -- it is also essential to achieving quantum error correction on a universal quantum computation. Qubit state measurements in a neutral atom array are achieved by probing the array with light detuned from a cycling transition and capturing resulting fluorescence with a high quantum efficiency imaging device, producing a greyscale image of the neutral atom array. Conventionally, to achieve a fidelity above 99%, the typical probing period is several ms. This is a significant delay, given that the longest gate operation only takes several micros. In this poster, we demonstrate qubit state measurements assisted by a supervised convolutional neural network (CNN) in a neutral atom quantum processor. We present two CNN architectures for analyzing neutral atom qubit readout data: a compact 5-layer single-qubit CNN architecture and a 6-layer multi-qubit CNN architecture. We benchmark both architectures against a conventional Gaussian threshold analysis method. We demonstrate up to 56% reduction of measurement infidelity using the CNN compared to a conventional analysis method. This work presents a proof of concept for a CNN network to be implemented as a real-time readout processing method on a neutral atom quantum computer, enabling faster readout time and improved fidelity.
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Repetitive readout and real-time control of nuclear spin qubits in 171Yb atoms
We demonstrate high fidelity repetitive projective measurements of nuclear spin qubits in an array of neutral ytterbium-171 (171Yb) atoms. We show that the qubit state can be measured with a fidelity of 0.995(4) under a condition that leaves it in the state corresponding to the measurement outcome with a probability of 0.993(6) for a single tweezer and 0.981(4) averaged over the array. This is accomplished by near-perfect cyclicity of one of the nuclear spin qubit states with an optically excited state under a magnetic field of B=58 G, resulting in a bright/dark contrast of ≈105 during fluorescence readout. The performance improves further as ∼1/B2. The state-averaged readout survival of 0.98(1) is limited by off-resonant scattering to dark states and can be addressed via post-selection by measuring the atom number at the end of the circuit, or during the circuit by performing a measurement of both qubit states. We combine projective measurements with high-fidelity rotations of the nuclear spin qubit via an AC magnetic field to explore several paradigmatic scenarios, including the non-commutivity of measurements in orthogonal bases, and the quantum Zeno mechanism in which measurements "freeze" coherent evolution. Finally, we employ real-time feedforward to repetitively deterministically prepare the qubit in the +z or −z direction after initializing it in an orthogonal basis and performing a projective measurement in the z-basis. These capabilities constitute an important step towards adaptive quantum circuits with atom arrays, such as in measurement-based quantum computation, fast many-body state preparation, holographic dynamics simulations, and quantum error correction.
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- PAR ID:
- 10432481
- Date Published:
- Journal Name:
- arXivorg
- Volume:
- 2305.02926
- ISSN:
- 2331-8422
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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