--- title: backends (latest version) description: API reference for qiskit_addon_mpf.backends in the latest version of qiskit-addon-mpf source: https://eu-de.quantum.cloud.ibm.com/docs/en/api/qiskit-addon-mpf/backends --- # Backends `qiskit_addon_mpf.backends` Optional backends for the [`DynamicMPF`](/docs/api/qiskit-addon-mpf/dynamic#dynamicmpf "qiskit_addon_mpf.dynamic.DynamicMPF") algorithm. ## Availability Whether a certain backend can be used depends on the availability of the underlying tensor network library. This can easily be asserted at runtime using the following indicators: ### HAS\_QUIMB Indicates whether the optional [`quimb`](https://quimb.readthedocs.io/en/latest/autoapi/quimb/index.html#module-quimb) dependency is installed. ### HAS\_TENPY Indicates whether the optional [`tenpy`](https://tenpy.readthedocs.io/en/latest/main.html#module-tenpy "(in TeNPy v1.0.5)") dependency is installed. ## Backends Depending on the availability (see above), the following backends are available: | | | | ------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------- | | [`quimb_tebd`](/docs/api/qiskit-addon-mpf/backends-quimb-tebd#module-qiskit_addon_mpf.backends.quimb_tebd "qiskit_addon_mpf.backends.quimb_tebd") | A [`quimb`](https://quimb.readthedocs.io/en/latest/autoapi/quimb/index.html#module-quimb)-based TEBD backend. | | [`quimb_layers`](/docs/api/qiskit-addon-mpf/backends-quimb-layers#module-qiskit_addon_mpf.backends.quimb_layers "qiskit_addon_mpf.backends.quimb_layers") | A layer-wise time-evolution backend using [`quimb`](https://quimb.readthedocs.io/en/latest/autoapi/quimb/index.html#module-quimb). | | [`quimb_circuit`](/docs/api/qiskit-addon-mpf/backends-quimb-circuit#module-qiskit_addon_mpf.backends.quimb_circuit "qiskit_addon_mpf.backends.quimb_circuit") | A circuit-based time-evolution backend using [`quimb`](https://quimb.readthedocs.io/en/latest/autoapi/quimb/index.html#module-quimb). | | [`tenpy_tebd`](/docs/api/qiskit-addon-mpf/backends-tenpy-tebd#module-qiskit_addon_mpf.backends.tenpy_tebd "qiskit_addon_mpf.backends.tenpy_tebd") | A [`tenpy`](https://tenpy.readthedocs.io/en/latest/main.html#module-tenpy "(in TeNPy v1.0.5)")-based TEBD backend. | | [`tenpy_layers`](/docs/api/qiskit-addon-mpf/backends-tenpy-layers#module-qiskit_addon_mpf.backends.tenpy_layers "qiskit_addon_mpf.backends.tenpy_layers") | A layer-wise time-evolution backend using [`tenpy`](https://tenpy.readthedocs.io/en/latest/main.html#module-tenpy "(in TeNPy v1.0.5)"). | ## Interface The interface implemented by any one of these optional backends is made up of the following classes: ### Evolver *class* `Evolver` [GitHub](https://github.com/Qiskit/qiskit-addon-mpf/tree/stable/0.3/qiskit_addon_mpf/backends/interface.py#L21-L52) Bases: [`ABC`](https://docs.python.org/3/library/abc.html#abc.ABC) The interface for the time-evolution algorithms used within [`DynamicMPF`](/docs/api/qiskit-addon-mpf/dynamic#dynamicmpf "qiskit_addon_mpf.dynamic.DynamicMPF"). This time-evolution interface is used by the [`DynamicMPF.lhs`](/docs/api/qiskit-addon-mpf/dynamic#lhs "qiskit_addon_mpf.dynamic.DynamicMPF.lhs") and [`DynamicMPF.rhs`](/docs/api/qiskit-addon-mpf/dynamic#rhs "qiskit_addon_mpf.dynamic.DynamicMPF.rhs") and should time-evolve a [`State`](#qiskit_addon_mpf.backends.State "qiskit_addon_mpf.backends.State") object under its hood. The exact mechanism of the algorithm is described in more detail in [`DynamicMPF`](/docs/api/qiskit-addon-mpf/dynamic#dynamicmpf "qiskit_addon_mpf.dynamic.DynamicMPF"), [`State`](#qiskit_addon_mpf.backends.State "qiskit_addon_mpf.backends.State"), and [`setup_dynamic_lse()`](/docs/api/qiskit-addon-mpf/dynamic#setup_dynamic_lse "qiskit_addon_mpf.dynamic.setup_dynamic_lse"). #### conjugate *abstract property* Type: `bool` Returns whether this time-evolver instance acts on the right-hand side. #### evolved\_time *abstract property* Type: `float` Returns the current evolution time. #### step *abstract* `step()` [GitHub](https://github.com/Qiskit/qiskit-addon-mpf/tree/stable/0.3/qiskit_addon_mpf/backends/interface.py#L30-L38) Perform a single time step of this time-evolution algorithm. This should act on the internally referenced [`State`](#qiskit_addon_mpf.backends.State "qiskit_addon_mpf.backends.State") object (for which no name is prescribed by this interface). Whether this time-evolution algorithm instance should evolve the [`State`](#qiskit_addon_mpf.backends.State "qiskit_addon_mpf.backends.State") from the left- or right-hand side, depends on the value of [`conjugate`](#qiskit_addon_mpf.backends.Evolver.conjugate "qiskit_addon_mpf.backends.Evolver.conjugate"). **Return type** None ### State *class* `State` [GitHub](https://github.com/Qiskit/qiskit-addon-mpf/tree/stable/0.3/qiskit_addon_mpf/backends/interface.py#L55-L117) Bases: [`ABC`](https://docs.python.org/3/library/abc.html#abc.ABC) The interface for the [`DynamicMPF.evolution_state`](/docs/api/qiskit-addon-mpf/dynamic#evolution_state "qiskit_addon_mpf.dynamic.DynamicMPF.evolution_state"). This time-evolution state is shared between the LHS and RHS [`Evolver`](#qiskit_addon_mpf.backends.Evolver "qiskit_addon_mpf.backends.Evolver") instances of the [`DynamicMPF`](/docs/api/qiskit-addon-mpf/dynamic#dynamicmpf "qiskit_addon_mpf.dynamic.DynamicMPF") instance. In most cases where a concrete backend implementing this interface is based on tensor networks, this state will be a matrix product operator (MPO). This is because most time-evolution algorithms would normally evolve a matrix product state (MPS) as shown pictorially below, where time evolution blocks (`U#`) are successively applied to a 1-dimensional MPS (`S#`). Here, the tensor network grows towards the right as time goes on. ```python MPS Evolution S0┄┄┲━━━━┱┄┄┄┄┄┄┄┄┲━━━━┱┄ │ ┃ U1 ┃ ┃ U5 ┃ S1┄┄┺━━━━┹┄┲━━━━┱┄┺━━━━┹┄ │ ┃ U3 ┃ S2┄┄┲━━━━┱┄┺━━━━┹┄┲━━━━┱┄ ... │ ┃ U2 ┃ ┃ U6 ┃ S3┄┄┺━━━━┹┄┲━━━━┱┄┺━━━━┹┄ │ ┃ U4 ┃ S4┄┄┄┄┄┄┄┄┄┺━━━━┹┄┄┄┄┄┄┄┄ ``` However, in our case, we want two time-evolution engines to share a single state. In order to achieve that, we can have one of them evolve the state from the right (just as before, `U#`), but have the second one evolve the state from the left (`V#`). This requires the state to also have bonds going of in that direction, rendering it a 2-dimensional MPO (`M#`) rather than the 1-dimensional MPS from before. ```python MPO Evolution ┄┲━━━━┱┄┄┄┄┄┄┄┄┲━━━━┱┄┄M0┄┄┲━━━━┱┄┄┄┄┄┄┄┄┲━━━━┱┄ ┃ V5 ┃ ┃ V1 ┃ │ ┃ U1 ┃ ┃ U5 ┃ ┄┺━━━━┹┄┲━━━━┱┄┺━━━━┹┄┄M1┄┄┺━━━━┹┄┲━━━━┱┄┺━━━━┹┄ ┃ V3 ┃ │ ┃ U3 ┃ ... ┄┲━━━━┱┄┺━━━━┹┄┲━━━━┱┄┄M2┄┄┲━━━━┱┄┺━━━━┹┄┲━━━━┱┄ ... ┃ V6 ┃ ┃ V2 ┃ │ ┃ U2 ┃ ┃ U6 ┃ ┄┺━━━━┹┄┲━━━━┱┄┺━━━━┹┄┄M3┄┄┺━━━━┹┄┲━━━━┱┄┺━━━━┹┄ ┃ V4 ┃ │ ┃ U4 ┃ ┄┄┄┄┄┄┄┄┺━━━━┹┄┄┄┄┄┄┄┄┄M4┄┄┄┄┄┄┄┄┄┺━━━━┹┄┄┄┄┄┄┄┄ ``` #### overlap *abstract* `overlap(initial_state)` [GitHub](https://github.com/Qiskit/qiskit-addon-mpf/tree/stable/0.3/qiskit_addon_mpf/backends/interface.py#L101-L117) Compute the overlap of this state with the provided initial state. > **Warning** > > A concrete implementation of this method should raise a [`TypeError`](https://docs.python.org/3/library/exceptions.html#TypeError) if the provided `initial_state` object is not supported by the implementing backend. **Parameters** **initial\_state** ([*Any*](https://docs.python.org/3/library/typing.html#typing.Any)) – the initial state with which to compute the overlap. **Raises** [**TypeError**](https://docs.python.org/3/library/exceptions.html#TypeError) – if the provided initial state has an incompatible type. **Returns** The overlap of this state with the provided one. **Return type** [complex](https://docs.python.org/3/library/functions.html#complex)