Rydberg Neutral-Atom Qubit

A neutral-atom qubit architecture where long-lived hyperfine ground states encode (|0\rangle, |1\rangle), and entangling interactions are turned on transiently by laser excitation to high-lying Rydberg states. This is the core hardware model for modern optical-tweezer neutral-atom processors.

Physics

Single-qubit states are typically encoded in hyperfine “clock” states of alkali atoms (e.g., (^{87}\mathrm{Rb}), (^{133}\mathrm{Cs})).

Two-qubit entangling gates exploit the Rydberg blockade effect: if one atom is excited to a Rydberg state, nearby atoms are shifted out of resonance, suppressing simultaneous excitation and enabling conditional dynamics.

Hamiltonian

A standard driven Rydberg-array Hamiltonian (rotating frame) is:

$H={\sum }_i\left[\frac{{\Omega }_i(t)}{2}{\sigma }_x^{(i)}-{\Delta }_i(t)n_i\right]+{\sum }_{i<j}{V}_{ij}{n}_i{n}_j$

where $n_i=|r{⟩}_i⟨r|$ projects onto the Rydberg state, ${\Omega }_i$ is the Rabi drive, ${\Delta }_i$ detuning, and $V_{ij}=C_6/R_{ij}^6$ (van der Waals) or $\propto 1/R_{ij}^3$ in resonant dipole regimes.

Blockade condition for two atoms $i,j$:

$V_{ij}\gg \Omega$

suppresses double excitation $|rr⟩$, enabling controlled-phase entangling gates.

Figure

Why it matters

• Native all-to-all reconfigurability (via tweezer rearrangement) at array level.
• Strong, switchable interactions for fast entangling gates.
• A direct path from analog simulation to digital gate-based computing on the same hardware family.

Key Metrics

Metric	Value	Notes	Fidelity reference
$T_1$ (qubit lifetime)	1–10 s	Hyperfine clock states in optical traps; vacuum-limited	Evered et al. 2023
$T_2$ (coherence)	1–4 s	With spin-echo; limited by trap-induced dephasing	Evered et al. 2023
1Q gate fidelity	99.5–99.90%	Global and local Raman gates	Evered et al. 2023
2Q gate fidelity (CZ)	99.5%	Rydberg blockade CZ; SOTA with erasure conversion	Evered et al. 2023
Gate time (2Q)	200–500 ns	Rydberg pulse sequence	Evered et al. 2023
Architecture scale	100–1000+ physical atoms	Optical tweezer arrays; reconfigurable	henriet-2020-quantum-computing-with-neutral, wu-2020-a-concise-review-of
2Q gate mechanism	Rydberg blockade	$C_6/R^6$ van der Waals interaction	jaksch-2000-rydberg-gate
Operating temperature	~10–50 μK	Laser-cooled; in ultrahigh vacuum	Evered et al. 2023
Fault-tolerant logical gate regime	Not yet established	Active experimental frontier	henriet-2020-quantum-computing-with-neutral

Linked Papers

• jaksch-2000-rydberg-gate
• henriet-2020-quantum-computing-with-neutral
• wu-2020-a-concise-review-of

Related Entries

• trapped-ion-qubit
• alkaline-earth-neutral-atom-clock-qubit
• nuclear-spin-neutral-atom-qubit