# Glossary¶

Expressions that are grouped together are used synonymously in the Strawberry Fields documentation.

- backend
Executes quantum programs. Can be either a classical simulator or a quantum hardware device, local or remote. Different backends can have different capabilities in terms of efficiency and which class of circuits they can execute. See:

`strawberryfields.backends.BaseBackend`

- circuit
- quantum circuit
- program
A sequence of quantum operations acting on a quantum register. Typically contains measurements that produce a stochastic classical output. Represents a quantum computation. See:

`strawberryfields.Program`

- circuit class
- circuit family
A well-defined subset of quantum circuits. Members of a given circuit class can potentially be evaluated on more than one backend, and each backend has an associated circuit class it can execute. See:

`strawberryfields.circuitspecs.CircuitSpecs`

- compilation
The process of converting a source quantum program into an equivalent program that belongs in the target circuit class. The compilation can fail if the program cannot be made equivalent to the target circuit class.

- equivalent circuit
- equivalent program
Two quantum circuits are equivalent iff they produce the same output probability distributions. Two equivalent circuits are not necessarily in the same circuit class.

- engine
A class for executing quantum programs on a specific backend. See:

`strawberryfields.engine.LocalEngine`

,`strawberryfields.RemoteEngine`

- frontend
All components of Strawberry Fields that are user-facing. Includes the user interface (engine, program, operation); excludes the backends. See:

`strawberryfields.Engine`

,`strawberryfields.Program`

,`Operation`

- gate
- quantum gate
A quantum operation that changes the state of the register. Analogous to a logic gate in a Boolean circuit.

- measurement
A quantum operation that returns classical information.

- operation
- quantum operation
Something that acts on specific subsystems of the register, changing its state and possibly returning classical information, e.g., a state preparation, gate, measurement, etc. See:

`Operation`

- register
- quantum register
- system
- mode
- qumode
A quantum system (or a simulation of one) storing the state of the quantum computation. Typically consists of several subsystems (which in CV quantum computing are called modes).

- state preparation
- preparation
An operation where a quantum system or subsystem is prepared in a known fixed state. Typically accomplished by applying a specific sequence of gates to a known reference state.

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