Quantum Computing with CS Atom Qubits

Quantum computing is being explored using several implementations for quantum bits (qubits) including: ions, superconducting Josephson junctions, quantum dots, photons, nitrogen vacancy centers in diamonds, and neutral atoms. Each candidate qubit has its strengths and weakness. This project will pursue several important steps towards scalable quantum computation with atoms. Neutral atoms trapped in optical lattices can be well-isolated from their environment, so they have relatively long coherence times, which is an essential feature for qubits. Trapping atoms with light presents a straightforward path for putting many qubits in the same system. This team has recently demonstrated high fidelity quantum gates involving single atoms, and has trapped exactly one atom at each of 50 lattice sites. This team will work to measure qubit states without particle loss. This team will also investigate ways to make the trapped atoms colder, which might enable new ways to entangle these atoms using collisions. Using improved methods to control and cool atoms, this team aims to dramatically improve the state of the art for entangling neutral atoms. Entanglement is an essential feature of quantum mechanics. For instance, if two identical particles can each be in either state A or B, they can be in the entangled state AA+BB, which means that the particles are in a superposition of both being in A or both being in B, while there is never one in A and the other in B. These highly non-classical states are central to the working of quantum computers. This is important because a quantum computer with >50 qubits could solve certain kinds of problems that are otherwise unsolvable.

This team will develop experimental techniques needed for a neutral atom quantum computer using cold atoms in a 3D optical lattice with 5 micron spacing between the lattice sites. They recently demonstrated perfect filling of 4x4x3 and 5x5x2 arrays, and the ability to perform single qubit gates at any site with 0.997 gate fidelity and little cross talk. For part of this grant period they will develop a new technique for measuring qubit states by coherently splitting atoms based on their internal states, and then locking them in place with a shorter length scale optical lattice. In this way their location encodes their initial internal state, which will allow them to distinguish atom loss from other errors. By dynamically switching to a deeper lattice, they will also attempt to improve atom cooling beyond the current situation with 90% of the population in the 3D vibrational ground state. If they can achieve better than 99%, it will open up the possibility of creating massive entanglement with a few collisions, which might allow for the realization of one-way quantum computing. While pursuing the above goals this team will work on demonstrating a novel form of two-qubit Rydberg gates, using a combination of ultraviolet and microwave photons. Adapting principles from their 3D addressing for one-qubit gates, they will explore ways to achieve site addressed fidelities comparable to the one-qubit gates. This would make a better quantum computer platform, and set the stage for more fully realizing the scalability potential of cold atom arrays.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.