# sf.ops.Thermal¶

class Thermal(n=0)[source]

Bases: strawberryfields.ops.Preparation

Prepare a mode in a thermal state.

The requested mode is traced out and replaced with the thermal state $$\rho(\bar{n})$$. As a result the state will be described using a density matrix.

Parameters

n (float) – mean thermal population of the mode

Definition

The thermal state is a mixed Gaussian state defined by

$\rho(\nbar) := \sum_{n=0}^\infty\frac{\nbar^n}{(1+\nbar)^{n+1}}\ketbra{n}{n}$

where $$\nbar:=\tr{(\rho(\nbar)\hat{n})}$$ is the mean photon number. In the Gaussian formulation one has $$\mathbf{V}=(2 \nbar +1) \frac{\hbar}{2} I$$ and $$\bar{\mathbf{r}}=(0,0)$$.

 measurement_deps Extra dependencies due to parameters that depend on measurements. ns
measurement_deps

Extra dependencies due to parameters that depend on measurements.

Returns

dependencies

Return type

set[RegRef]

ns = 1
 apply(reg, backend, **kwargs) Ask a local backend to execute the operation on the current register state right away. decompose(reg, **kwargs) Decompose the operation into elementary operations supported by the backend API. merge(other) Merge the operation with another (acting on the exact same set of subsystems).
apply(reg, backend, **kwargs)

Ask a local backend to execute the operation on the current register state right away.

Takes care of parameter evaluations and any pending formal transformations (like dagger) and then calls Operation._apply().

Parameters
• reg (Sequence[RegRef]) – subsystem(s) the operation is acting on

• backend (BaseBackend) – backend to execute the operation

Returns

the result of self._apply

Return type

Any

decompose(reg, **kwargs)

Decompose the operation into elementary operations supported by the backend API.

See strawberryfields.backends.base.

Parameters

reg (Sequence[RegRef]) – subsystems the operation is acting on

Returns

decomposition as a list of operations acting on specific subsystems

Return type

list[Command]

merge(other)

Merge the operation with another (acting on the exact same set of subsystems).

Note

For subclass overrides: merge may return a newly created object, or self, or other, but it must never modify self or other because the same Operation objects may be also used elsewhere.

Parameters

other (Operation) – operation to merge this one with

Returns

other * self. The return value None represents the identity gate (doing nothing).

Return type

Operation, None

Raises

MergeFailure – if the two operations cannot be merged