Backends

What a Backend Is

In Tessera, a backend is an entry in the backend registry that defines three things:

Component	Description
Basis gate set	The set of gate names natively supported by the hardware
Decomposition map	A map from non-basis gate names to equivalent sequences of basis gates
Default coupling map	The hardware topology used for routing when no override is provided

When you pass backend="IBM" to transpile(), Tessera looks up the IBM entry in the registry, uses its basis gate set to determine what needs decomposing, its decomposition map to perform those decompositions, and its default coupling map for qubit layout and routing.

IBM

Basis gates: cx, rz, sx, x, u
Default device: FakeNairobiV2: 7 qubits, heavy-hex topology
Registry key: "IBM"

Available coupling maps

Key	Device	Qubits	Topology
`IBM_DEFAULT`	FakeNairobiV2	7	Heavy-hex
`IBM_BRISBANE`	FakeBrisbane	127	Heavy-hex
`IBM_SHERBROOKE`	FakeSherbrooke	127	Heavy-hex

# Default (FakeNairobiV2, 7 qubits)
transpile(qc, backend="IBM")

# Brisbane (127 qubits)
transpile(qc, backend="IBM", coupling_map="IBM_BRISBANE")

# Sherbrooke (127 qubits)
transpile(qc, backend="IBM", coupling_map="IBM_SHERBROOKE")

IBM coupling maps are derived from real hardware topologies via Qiskit's fake provider backends.

IonQ

Basis gates: rx, ry, rz, cx
Default device: Aria: 25 qubits, all-to-all topology
Registry key: "IONQ"

Available coupling maps

Key	Device	Qubits	Topology
`IONQ_ARIA`	IonQ Aria	25	All-to-all
`IONQ_FORTE`	IonQ Forte	36	All-to-all

# Default (Aria, 25 qubits)
transpile(qc, backend="IONQ")

# Forte (36 qubits)
transpile(qc, backend="IONQ", coupling_map="IONQ_FORTE")

Note

IonQ hardware uses an all-to-all topology, so every qubit is directly connected to every other qubit. This means BasicSwapRouter will never need to insert SWAP gates for IonQ circuits regardless of the circuit structure. The routing pass still runs but is effectively a no-op.

Rigetti

Basis gates: rx, rz, cz
Default device: Ankaa-2: 84 qubits, rectangular grid topology
Registry key: "RIGETTI"

Available coupling maps

Key	Device	Qubits	Topology
`RIGETTI_ANKAA`	Rigetti Ankaa-2	84	7×12 rectangular grid
`RIGETTI_ANKAA_9Q`	Rigetti Ankaa-9Q-3	9	3×3 rectangular grid

# Default (Ankaa-2, 84 qubits)
transpile(qc, backend="RIGETTI")

# Ankaa-9Q-3 (9 qubits, useful for small circuit testing)
transpile(qc, backend="RIGETTI", coupling_map="RIGETTI_ANKAA_9Q")

Note

cx is not in Rigetti's basis gate set. Any cx gate, whether in the input circuit or introduced during decomposition, is inlined as H·CZ·H (H gate, CZ gate, H gate) since cz is the native two-qubit gate. This is handled automatically by the decomposition map.

Backend and Coupling Map Independence

The backend and coupling map are fully independent in Tessera. The backend controls only gate decomposition, including which gates need to be broken down and how. The coupling map controls only routing topology, including which qubits are adjacent and how SWAPs are inserted. There is no validation tying them together.

This means you can freely mix any backend with any coupling map:

# Decompose to IBM basis gates but route using IonQ's all-to-all topology
transpile(qc, backend="IBM", coupling_map="IONQ_ARIA")

# Decompose to Rigetti basis gates but route on a small 9-qubit grid
transpile(qc, backend="RIGETTI", coupling_map="RIGETTI_ANKAA_9Q")

In practice you'll almost always use a coupling map that matches your backend's hardware, but the separation is intentional because it keeps the two concerns cleanly isolated and makes both easier to test and extend independently.

Using a Non-Default Coupling Map

Pass any registry key string or a TesseraCouplingMap instance directly to transpile():

# Named key
transpile(qc, backend="IBM", coupling_map="IBM_BRISBANE")

# Custom coupling map
from tessera.hardware.coupling_map import TesseraCouplingMap

cm = TesseraCouplingMap(4, [(0,1),(1,0),(1,2),(2,1),(2,3),(3,2)])
transpile(qc, backend="IBM", coupling_map=cm)

See the Coupling Maps page for the full list of available registry keys and details on building custom topologies.

Adding a New Backend

Tessera's backend registry is designed to be extended with minimal friction. adding a new backend touches only a handful of files and requires no changes to any pass. See the Adding a Backend guide for a full step-by-step walkthrough.