35 |
HFSS-C-001 |
ZZ Coupling ζ (idle) |
Critical |
ζ_ZZ/2π < 10 kHz between non-coupled pairs (idle) |
< 1 kHz |
1 – 100 kHz |
- < 1 kHz: conditional phase < 0.01 rad in 10 µs; negligible idle ZZ
error
|
- > 1 MHz: > 1 rad conditional phase per µs; circuit depth severely
limited
|
- Always-on ZZ interaction from dispersive coupling. Even static ZZ causes
phase errors that accumulate, limiting circuit depth.
|
36 |
HFSS-C-002 |
Nearest Neighbour Isolation |
High |
S_ij (nearest neighbour) ≤ −40 dB |
< −40 dB |
−30 to −50 dB |
- < −40 dB: driven rotation on neighbour qubit < 10⁻⁴ rad during
single-qubit gate
|
- > −20 dB: significant driven rotation on neighbours; simultaneous
single-qubit gates not independent
|
- EM isolation between nearest-neighbour qubits. Insufficient isolation causes
unwanted rotations during single-qubit gates.
|
37 |
HFSS-C-003 |
Next-Nearest Isolation |
High |
S_ij (next-nearest) ≤ −60 dB |
< −60 dB |
−50 to −70 dB |
- < −60 dB: long-range crosstalk < 10⁻⁶ rad; 2D grid operation fully
independent
|
- > −40 dB: long-range coupling; frequency collisions compound with
nearest-neighbour
|
- Isolation beyond nearest neighbour. Critical for scalable multi-qubit
processors; long-range EM leakage compounds errors.
|
38 |
HFSS-C-004 |
Leakage to |2⟩ (L₁) |
Critical |
L₁ < 0.01% per gate |
< 0.01 % |
0.01 – 0.1 % |
< 0.01%: seepage outside qubit subspace negligible; DRAG pulse sufficient |
- > 1%: leakage accumulates over circuit; error correction cannot track
non-qubit states
|
- Population leaked to |2⟩ non-computational state during gates. DRAG pulses
mitigate but require sufficient anharmonicity.
|
39 |
HFSS-C-005 |
Spurious Mode Gap Δf_spur |
High |
Δf_spur ≥ 1 GHz from nearest spurious EM mode |
> 1 GHz gap |
0.5 – 2 GHz gap |
- > 1 GHz gap: no spurious mode within pulse bandwidth; gate calibration
stable
|
- < 0.2 GHz: mode within pulse bandwidth; state leakage and parametric
drive of spurious modes
|
- Frequency distance to nearest unintended EM mode. Modes within drive
bandwidth cause state leakage and gate calibration drift.
|
40 |
HFSS-C-006 |
Package Mode Density |
Medium |
< 1 spurious package mode per GHz near qubit band |
< 0.5 modes/GHz |
< 5 modes/GHz |
- < 0.5/GHz: low probability of accidental hybridisation across 64-qubit
chip
|
- > 10/GHz: dense mode spectrum; unavoidable hybridisation; package must be
redesigned
|
- Density of package/enclosure modes near qubit frequency. High density
increases probability of accidental mode hybridisation.
|