Semiconducting MOC

Curated map of Zoo entries in the Semiconducting family.

Entries

Entry	Type	Status
aeon-qubit	qubit	demonstrated
exchange-only-qubit	qubit	demonstrated
flip-flop-qubit	qubit	demonstrated
hole-spin-qubit	qubit	demonstrated
hybrid-qubit	qubit	demonstrated
kane-qubit	qubit	demonstrated
rx-qubit	qubit	demonstrated
semiconductor-charge-qubit	qubit	demonstrated
silicon-spin-qubit	qubit	demonstrated
loss-divincenzo-qubit	qubit	demonstrated
singlet-triplet-qubit	qubit	demonstrated
spin-qubit	qubit	demonstrated

Composition

• qubit: 12

Conceptual anchors

• exchange-interaction-in-quantum-dots is the device-level primitive for the whole dot-defined branch: it explains where tunable $J$ actually comes from and why barrier control became the preferred route.
• heisenberg-exchange-in-quantum-dots is the algebraic companion note for the encoded-spin branch, where the main question is no longer how $J$ is made but what logical axis an exchange pulse implements.
• decoherence-free-subspace is the clean separator between simple one-spin / two-spin notes and the three-spin encoded branch.
• charge-noise-sweet-spot is the main cross-cutting lens for the whole family whenever electrical tunability starts pulling charge sensitivity back in.
• spin-orbit-coupling-for-qubit-control marks the main fork between electron-spin platforms that need synthetic gradients and hole-spin platforms that get direct electrical drive from strong SOC.

Curated synthesis

The highest-value organizing move in this family is to separate the single-spin baseline from the encoded-exchange ladder and from the charge-admixed side branches. Otherwise loss-divincenzo-qubit, singlet-triplet-qubit, exchange-only-qubit, rx-qubit, and aeon-qubit blur into “more spin qubits” when they are actually different answers to the same control-versus-noise problem.

1. The baseline branch is local-spin-first

   • loss-divincenzo-qubit is the minimal recipe: one spin per dot, exchange for entangling gates, and extra engineering for fast one-qubit control.
   • spin-qubit and silicon-spin-qubit should stay as umbrella notes for the broader modality and materials trajectory, not absorb the encoded-spin descendants.

2. The encoded-exchange ladder adds symmetry structure step by step

   • singlet-triplet-qubit is the first compression move: two spins, one encoded qubit, exchange as a logical splitting instead of only a two-qubit gate primitive.
   • exchange-only-qubit pushes that idea into a true three-spin encoded subsystem, removing the need for microwave drive or field gradients at the price of more elaborate pulse geometry.
   • rx-qubit keeps the three-spin encoding but moves into an always-on, resonantly driven regime to gain a sweet-spot operating mode and cavity-friendly control.
   • aeon-qubit is the endpoint of this local ladder: keep exchange always on, stay at a double sweet spot, and turn barrier-gate tuning into the main control surface.
   • Read this whole branch by alternating between exchange-interaction-in-quantum-dots for the physical origin of $J$ and heisenberg-exchange-in-quantum-dots for the logical action of that coupling after projection.

3. The side branches are different compromises, not incomplete versions of the ladder

   • semiconductor-charge-qubit and hybrid-qubit buy speed by re-admitting charge character into the qubit itself.
   • hole-spin-qubit uses strong intrinsic SOC to make electrical control native rather than synthetic.
   • kane-qubit is the donor-spin branch, where atomic placement and hyperfine control replace lithographic quantum-dot tuning as the defining resource.
   • flip-flop-qubit is the donor-interface extension: the electron–nuclear encoding and microwave-electric one-qubit control are now demonstrated, but the large donor–interface dipole, 180–500 nm logical coupling, and two-qubit gate remain proposal-stage. Keep those evidence layers separate.

Exchange-control routing matrix

The dot-defined entries are easiest to distinguish by following the same physical resource through three layers: encoding, control regime, and residual cost. This table is a routing aid, not a performance ranking.

Entry	Logical encoding	What exchange / charge motion does	Protection or control advantage	Residual architectural cost
loss-divincenzo-qubit	One electron spin per dot	A pulsed interdot exchange coupling supplies the native two-spin entangler	Minimal encoding overhead; local spin control and exchange entangling gates stay conceptually separate	Requires a separate one-qubit drive mechanism plus calibrated, low-crosstalk exchange pulses
singlet-triplet-qubit	Two spins in the ${	S\rangle,	T_0\rangle}$ subspace	Exchange becomes a logical splitting; a field gradient supplies the second rotation axis
exchange-only-qubit	Three-spin decoherence-free subsystem	Pairwise exchange generates non-collinear logical axes, using serial or simultaneous baseband pulses	No microwave drive or engineered field gradient is required; uniform magnetic noise acts mainly on the gauge subsystem	Encoded entangling gates are pulse-heavy, while local gradients, charge noise, leakage, and calibration crosstalk remain
rx-qubit	The same three-spin encoded manifold	Always-on symmetric exchange defines the splitting; resonant exchange modulation drives gates	Operates at a detuning sweet spot and couples naturally to resonators	Requires phase-locked RF control and accepts an always-on precession / interaction budget
aeon-qubit	Three spins with always-on nearest-neighbor exchange	Barrier-gate modulation steers simultaneous exchange while remaining at a double detuning sweet spot	Baseband universal control can stay first-order insensitive to both detuning coordinates	The protected point has no transverse electric dipole, complicating ordinary cavity coupling and long-range interconnects
hybrid-qubit	Three-electron charge-spin states in a double dot	Detuning and tunnel coupling deliberately mix charge sectors to enable very fast electrical gates	Compact footprint and strong electric controllability, with useful protected operating points	Charge sensitivity and leakage are reduced rather than removed; the speed gain has not translated into leading spin-qubit fidelity

Read the first two columns through exchange-interaction-in-quantum-dots when the question is how the gates manufacture $J$. Read the third and fourth columns through heisenberg-exchange-in-quantum-dots, decoherence-free-subspace, and charge-noise-sweet-spot when the question is what that coupling becomes after projection and which noise channel survives.

Donor branch evidence ladder

The donor entries are easiest to misread when a demonstrated local operation is allowed to validate a more ambitious coupling architecture. Route them by asking which layer has actually crossed from proposal to hardware.

Entry	Demonstrated core	Scaling mechanism under test	Claim that must remain separate
kane-qubit	Individual phosphorus electron/nuclear-spin control, ultralong nuclear memory, exchange-mediated gates, and multi-qubit donor processors	Atomically placed donors with hyperfine addressability and short-range electron exchange	Demonstrated donor processors validate the Kane lineage, but do not remove the placement and dense-control burden of local exchange
flip-flop-qubit	The electron–nuclear flip-flop transition and microwave-electric one-qubit control in a single implanted donor	Gate-controlled donor–interface orbital admixture intended to create a strong electric dipole and relax donor-spacing constraints	The donor–interface ionization point, predicted 180–500 nm dipole coupling, resonator-mediated extension, and any flip-flop two-qubit gate remain undemonstrated

Use coherence-time-hierarchy to keep Kane’s nuclear-memory record distinct from the coherence of an electrically hybridized flip-flop transition. Use charge-noise-sweet-spot for the flip-flop design tension: the same orbital admixture that makes long-range electrical coupling possible also imports interface-charge noise. Finally, use resonator-as-quantum-bus only for the proposed microwave extension beyond direct dipole coupling, not as evidence that the local donor–interface gate has already been realized.

Donor coupling-mechanism guardrail

The donor lineage does not inherit one generic “exchange gate.” kane-qubit uses a J-gate to tune approximately isotropic Heisenberg exchange between neighboring donor electrons; after the electron-mediated nuclear-spin sequence is reduced to its gate primitive, exchange-interaction-in-quantum-dots, heisenberg-exchange-in-quantum-dots, and sqrt-swap-as-universal-gate are the relevant conceptual chain.

flip-flop-qubit was proposed specifically to relax that short-range placement constraint. Donor–interface orbital admixture gives each encoded electron–nuclear transition an electric dipole, and two such qubits interact through a projected dipole–dipole XY / flip-flop coupling. Its predicted entangler is therefore in the $\sqrt{\mathrm{iSWAP}}$ family, not the isotropic $\sqrt{\mathrm{SWAP}}$ family. Read sqrt-swap-as-universal-gate only for its explicit SWAP-versus-iSWAP boundary, and do not route the proposed 180–500 nm coupling through the quantum-dot Heisenberg-exchange notes.

This distinction matters architecturally: Kane pays atomic-placement and short-range-overlap costs to obtain exchange, whereas the flip-flop proposal deliberately borrows charge character to obtain range and then pays in interface-noise exposure. Similar gate names do not make those coupling mechanisms interchangeable.

Routing rule: when to enter which note

• Enter spin-qubit or silicon-spin-qubit when the question is platform-level competitiveness, fabrication trajectory, or the overall semiconductor pitch.
• Enter loss-divincenzo-qubit when you want the cleanest “single spin + exchange” template.
• Enter singlet-triplet-qubit, exchange-only-qubit, rx-qubit, and aeon-qubit as a sequence when the real comparison is how much encoding and sweet-spot structure is being introduced to civilize exchange control.
• Enter semiconductor-charge-qubit, hybrid-qubit, or hole-spin-qubit when the main tradeoff is faster electrical control versus renewed charge sensitivity.
• Enter kane-qubit when the donor story is atomic placement, hyperfine addressability, and demonstrated short-range exchange; enter flip-flop-qubit when the question is whether orbital admixture can trade that placement burden for electrically mediated range.
• For semiconductor descendants that cross fully into Josephson-circuit territory, continue in super-semi-moc.