Nuclear-Spin Neutral-Atom Qubit

Figure

Description

Nuclear-spin neutral-atom qubits encode logical states in long-lived nuclear spin manifolds of alkaline-earth(-like) atoms such as ${}^{87}$Sr ($I=9/2$) or ${}^{171}$Yb ($I=1/2$), exploiting reduced magnetic sensitivity and ultra-narrow optical transitions. The key idea is a coherence-first strategy: logical information is stored in weakly magnetically sensitive nuclear spin states within the ${}^1{S}_0$ ground-state manifold, while excited-state manifolds (Rydberg or optical-clock ${}^3{P}_0$ transitions) are accessed transiently for fast entanglement and control.

For ${}^{87}$Sr, the $F=9/2$ ground-state manifold provides 10 nuclear spin sublevels ($m_F=-9/2$ to $+9/2$). Qubit states can be chosen as magnetically insensitive pairs (e.g., $m_F=\pm 1/2$), where the differential Zeeman shift vanishes to first order. This architecture cleanly separates “memory” and “interaction” roles to reduce crosstalk, and is compatible with both optical tweezer and lattice implementations.

Hamiltonian

Effective two-level encoding with weak magnetic sensitivity:

$H=\frac{{\omega }_0}{2}{\sigma }_z+\frac{\Omega (t)}{2}{\sigma }_x+\delta (t)\frac{1-{\sigma }_z}{2}$

with design target $\partial {\omega }_0/\partial B\approx 0$ at operating points, where ${\omega }_0$ is the qubit splitting, $\Omega (t)$ is the control field Rabi frequency, and $\delta (t)$ is the detuning.

Motivation

Nuclear-spin encodings are a coherence-first strategy for neutral-atom computing. By pushing logical storage into weakly magnetically sensitive manifolds, these architectures can extend memory lifetimes while still using excited-state manifolds (Rydberg or optical-clock transitions) for fast entanglement and control. This provides:

• Long-lived storage with robust idle behavior
• Architecture-level separation of memory and interaction states to reduce crosstalk
• Compatibility with both tweezer and lattice implementations
• A promising route for modular networked neutral-atom processors

Experimental Status

Quantum computing proposal — Daley et al. (2008):

• Proposed quantum computing with alkaline-earth atoms using nuclear spin encoding
• Identified state-dependent lattice potentials as a key control primitive

High-fidelity entanglement — Madjarov et al. (2020):

• Demonstrated high-fidelity entanglement and detection of alkaline-earth Rydberg atoms (${}^{88}$Sr)
• Validated the Rydberg entanglement pathway for alkaline-earth platforms

Nuclear spin coherence demonstrations:

• Nuclear spin manifolds in ${}^{87}$Sr and ${}^{171}$Yb confirmed to support long-lived storage
• Compatible architectures demonstrated in multiple groups (Kaufman, Thompson, Ye)

Key Metrics

Metric	Value	Notes	Fidelity reference
Coherence potential	Very long (clock-state limited)	Primary motivation for encoding choice	Daley et al. 2008
Gate strategy	Raman / optical-clock transitions	Platform dependent	—
Entangling mechanism	Rydberg or cavity-mediated	Architecture dependent	Madjarov et al. 2020
Main challenge	Balancing coherence and gate speed	Open optimization frontier	—

References

Original proposal

• A. J. Daley et al., “Quantum Computing with Alkaline-Earth-Metal Atoms,” Phys. Rev. Lett. 101, 170504 (2008)

Architecture development

• A. J. Daley, J. Ye, and P. Zoller, “State-dependent lattices for quantum computing with alkaline-earth-metal atoms,” Eur. Phys. J. D 65, 207 (2011)

Experimental demonstrations

• I. S. Madjarov et al., “High-fidelity entanglement and detection of alkaline-earth Rydberg atoms,” Nat. Phys. 16, 857 (2020)

Linked Papers

• ma-2022-nuclear-spin-atom

Related Entries

• alkaline-earth-neutral-atom-clock-qubit — closely related clock-state encoding
• rydberg-neutral-atom-qubit — alkali Rydberg platform with complementary trade-offs