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The scale-up challenge facing quantum computing (QC) is daunting and varied. Its commonly held that 1 million qubits (or more) will be needed to deliver practical fault tolerant QC. Its also a varied challenge because today there are many qubit types (superconducting, trapped ion, neutral atom, photonics, topological, quantum dots, etc.) each facing very different scale-up approaches; for example in solid state systems part of the challenge typically involves efficient interconnecting of stationary qubits, while neutral atom- and trapped ion-based systems can require actually moving the qubits around.

Recently, neutral atom specialist Atom Computing reported developing techniques that now permits it to full load an array of 1225 sites with its qubits, neutral atoms. Atom posted a paper in late January on the work, explaining some of the technical details. Atom first reported creating a 1225-site array with 1180 occupied sites last fall claiming to be the first to break the 1000 qubit threshold.

The new paper sheds more detail on Atoms approach for scaling up its arrays, which the company says is a significant step on its path to effective scaling and error correction.

In this protocol, the tweezers provide microscopic rearrangement of atoms, while the cavity-enhanced lattices enable the creation of large numbers of deep optical potentials that allow for rapid low-loss imaging of atoms. We apply this protocol to demonstrate deterministic filling (99% per-site occupancy) of 1225-site arrays. Because the reservoir is repeatedly filled with fresh atoms, the array can be maintained in a filled state indefinitely. We anticipate that this protocol will be compatible with mid-circuit reloading, which will be a key capability for running large-scale error-corrected quantum computations whose durations exceed the lifetime of a single atom in the system, write the researchers.

Currently the range of qubit-counts on quantum processors varies from single digits to hundreds. In December, IBM, whose QCs use superconducting qubits, introduced an 1121-qubit Condor QPU (not yet available) and a smaller 133-qubit Heron QPU thats optimized for combining with multiple QPUs into larger quantum systems. QuEra, another neutral atom-based QC developer, has a 256-qubit (Aquila) device, and in January it showcased a roadmap QuEra says will lead to 10,000 physical qubits and 100 logical qubits in the 2026 time-frame.

The race is on to scale up physical qubit counts and logical qubit counts (comprised of many physical qubits to implement error correction).

Heres a brief description from the paper:

Typically, tweezer rearrangement is performed by stochastically loading up to a single atom into each trap within an array, imaging the atoms to determine trap occupancy, and then rearranging atoms within the array to create a deterministically occupied sub-array. Crucially, the number of atoms contained in the final array with this approach is no greater than the number initially loaded. Further, because the initial loading is stochastic, the number of sites in the array must generally be substantially larger than de- sired final sub-array (though under certain conditions, near-deterministic loading can be achieved).

Recently, repeated loading of a buffer array from an optical dipole trap reservoir has demonstrated that one can decouple the filling of a six-site target array from a single loading of a cold reservoir. In this work, we ex- tend this concept to repeated loading of a reservoir array, from which we create a deterministically filled target array (typically 99% occupancy) of over 1200 171Yb atoms in 1225 sites. This is made possible by combining optical tweezer arrays with a cavity-enhanced optical lattice to provide both microscopic control and the large number of deep traps required for rapid, high-fidelity, low-loss imaging of large numbers of atoms.

The paper is best read in full.

Link to Atom Computing paper (Iterative assembly of 171Yb atom arrays in cavity-enhanced optical lattices), https://arxiv.org/abs/2401.16177

Top image: Atom Computings neutral atom-based quantum system. Source: Atom Computing

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Atom Computing Reports Advance in Scaling Up Neutral Atom Qubit Arrays - HPCwire