Atoms Interact in Threes, Opening New Paths to Quantum Computing

A new method engineers strong three-body interactions within programmable Rydberg atom arrays, a key step towards more powerful quantum simulation. Rhine Samajdar and colleagues at Princeton University, in a collaboration between Princeton University, Harvard University, and Purdue University, have developed an experimentally accessible scheme to move beyond the typical two-body couplings found in these systems. The advancement fundamentally alters the underlying physics, enabling investigation of emergent quantum phases and ultimately simulation of a wider range of complex models from condensed matter and high-energy physics.

Enhanced Rydberg atom interactions reveal strong three-body coupling regimes

Three-body interactions now exceed two-body couplings by a factor of three, a threshold previously unattainable due to limitations in controlling atomic interactions beyond pairwise engagements. This breakthrough enables systematic investigation of the many-body Hamiltonian, unlocking access to emergent quantum phases inaccessible with traditional two-body systems; these phases are important for modelling complex physical systems. Scientists at Harvard University, the Massachusetts Institute of Technology and the University of California, Berkeley can explore a broader range of correlated models relevant to condensed matter and high-energy physics, expanding the scope of quantum simulation by engineering these stronger interactions within Rydberg atom arrays. The significance of this lies in the ability to move beyond approximations often necessary when dealing with strongly correlated quantum systems, allowing for more accurate and detailed simulations of phenomena like high-temperature superconductivity or exotic magnetic states.

The Rydberg lattice size, denoted as N, remains unspecified, prompting consideration of how readily this technique can be expanded to simulate larger, more realistic systems. Scaling these systems to larger N is crucial for tackling computationally challenging problems and reducing finite-size effects that can distort simulation results. Carefully tuned detunings, subtle energy adjustments, enhance interactions between triplets of atoms, bypassing the constraints of earlier methods reliant on time-dependent driving forces. These time-dependent methods, such as Floquet driving, often introduce unwanted heating and decoherence, limiting the coherence time of the quantum simulation. Calculations reveal these three-body forces are demonstrably larger than binary van der Waals interactions, particularly when tuned near an avoided crossing in the potential energy surface. Controlling the energy levels of atoms arranged in a lattice achieves this enhancement, specifically by detuning the laser on one sublattice to resonate with a chosen Rydberg state, creating a pathway for stronger couplings via states like |sss⟩ transitioning to |spp⟩. This precise control over the atomic energy landscape is achieved through a combination of optical and microwave control fields. Numerical modelling of three-atom interactions confirms a splitting of energy levels on the order of the dipole interaction strengths V13 and V23, indicating a genuinely multi-body effect; this is achieved using rubidium atoms excited to states including |37S−1/2, 37S−1/2, 38S−1/2⟩, offering a near-zero Forster defect. The Forster defect, a measure of the deviation from ideal dipole-dipole interactions, is minimised through careful selection of Rydberg states, ensuring the fidelity of the engineered interactions.

Engineered three-atom interactions within site-controlled Rydberg lattices

Manipulating interactions between atoms is central to building powerful quantum technologies, and a refined technique now allows unprecedented precision in this manipulation. A precisely arranged grid of atoms, similar to the arrangement of cells in a honeycomb, forms the Rydberg lattice where neutral atoms are carefully positioned. These atoms are typically trapped using optical tweezers, allowing for individual addressing and rearrangement. Site-controlled detunings enable the engineering of three-atom interactions, moving beyond the more common two-atom couplings. This is accomplished by selectively addressing individual sites within the lattice with laser light, altering the energy levels of the atoms at those locations. This approach offers a static and stable system for manipulating atomic interactions, avoiding the heating effects associated with time-dependent protocols like Floquet driving. Static control is particularly important for long-duration quantum simulations, where maintaining coherence is paramount. The lattice geometry, and the spacing between atoms, are also critical parameters influencing the strength and nature of the interactions.

Engineered three-body interactions advance Rydberg atom lattice quantum simulation

Vital for expanding the reach of quantum simulation, control over many-body interactions has historically been a considerable hurdle. Demonstrating these stronger interactions allows systematic investigation of the many-body Hamiltonian and reveals emergent quantum phases not accessible with two-body systems. The many-body Hamiltonian describes the total energy of the system, including all interactions between the atoms. Rydberg atoms are a promising technology for both quantum computing and simulation, functioning as qubits, the building blocks of quantum devices, and interacting via electrical forces. These interactions arise from the strong dipole moments induced when atoms are excited to Rydberg states. Previously, these lattices, arrangements of neutral atoms functioning as qubits, relied on simpler two-atom couplings, but this new method expands the possibilities for modelling complex quantum behaviours. The ability to engineer three-body interactions opens up new avenues for exploring phenomena such as many-body localisation, where quantum systems can become trapped in insulating states despite the presence of disorder, and fractional quantum Hall physics, which exhibits exotic emergent properties. Furthermore, the precise control offered by this technique could facilitate the development of novel quantum algorithms and error correction schemes, paving the way for more robust and scalable quantum computers.

The researchers successfully engineered three-body interactions within a lattice of neutral Rydberg atoms, moving beyond the previously limited two-body couplings. This achievement matters because it allows for the quantum simulation of a wider range of complex physical models, including those found in condensed matter and high-energy physics. By systematically investigating the resulting many-body Hamiltonian, they observed emergent quantum phases not previously attainable in these systems. The authors suggest this capability will broaden the scope of quantum simulation possible with Rydberg atom lattices.