Neutral Atom
Qubits encoded in neutral atoms held by optical tweezers, offering large-scale arrays and reconfigurable connectivity.
Neutral atom quantum computers trap individual atoms using focused laser beams (optical tweezers) and encode qubits in their electronic states. They’ve emerged as a promising platform for large-scale quantum computing.
How It Works
Trapping
- Optical tweezers: Focused laser beams create potential wells
- Atoms are trapped at intensity maxima (for red-detuned light)
- Can create 2D or 3D arrays with hundreds of atoms
Qubit Encoding
Typically use:
- Ground state:
- Rydberg state: (highly excited state)
Or hyperfine states in the ground manifold.
Rydberg Interactions
The key to two-qubit gates: Rydberg blockade.
When one atom is in the Rydberg state:
- Nearby atoms are shifted out of resonance
- Creates effective long-range interaction
- Range: several micrometers
This enables fast two-qubit gates.
Operations
Single-Qubit Gates
- Global laser pulses for all qubits
- Local addressing for individual control
- Microwave or Raman transitions
Two-Qubit Gates
- Excite both atoms to Rydberg states
- Blockade creates controlled phase
- CZ gates demonstrated with high fidelity
Readout
- Fluorescence imaging
- Atoms in certain states scatter light, others don’t
- Camera captures array snapshot
Advantages
| Advantage | Details |
|---|---|
| Scalability | Arrays of 1000+ atoms demonstrated |
| Identical qubits | All atoms of same isotope are identical |
| Reconfigurable | Can rearrange atoms with tweezers |
| Long coherence | T2 > 1 second possible |
| All-to-all connectivity | Rydberg interactions can be long-range |
Specifications
| Parameter | Typical Value |
|---|---|
| Array size | 100-1000+ atoms |
| T1 time | Seconds |
| T2 time | Milliseconds to seconds |
| 1-qubit fidelity | >99.5% |
| 2-qubit fidelity | >99% |
| Gate time | ~μs |
Challenges
| Challenge | Issue |
|---|---|
| Atom loss | Atoms occasionally escape traps |
| Motional heating | Atoms gain energy |
| Crosstalk | Rydberg interactions with unintended neighbors |
| Imaging resolution | Must distinguish closely spaced atoms |
Major Players
- QuEra Computing: Boston-based, public access
- Pasqal: French, 2D and 3D arrays
- Atom Computing: Long coherence focus
- Many university groups: Harvard, Caltech, JILA
Unique Capabilities
Native Multi-Qubit Gates
Rydberg interactions can implement gates on 3+ qubits natively.
Analog Quantum Simulation
Arrays naturally simulate spin models.
Reconfigurability
Can physically move atoms to change connectivity mid-computation.
See also: Qubit, Trapped Ion, Quantum Simulation