page_title: Quantum logic gate
section_title: Parallel gates
hierarchical_section_title: Quantum logic gate / Circuit composition / Parallel gates
caption_attribution_description: English: Describes how to treat parallel circuits of quantum logic gates
context_page_description: In quantum computing and specifically the quantum circuit model of computation, a quantum logic gate is a basic quantum circuit operating on a small number of qubits. They are the building blocks of quantum circuits, like classical logic gates are for conventional digital circuits.
  Unlike many classical logic gates, quantum logic gates are reversible. However, it is possible to perform classical computing using only reversible gates. For example, the reversible Toffoli gate can implement all Boolean functions, often at the cost of having to use ancilla bits. The Toffoli gate has a direct quantum equivalent, showing that quantum circuits can perform all operations performed by classical circuits.
context_section_description: The tensor product (or kronecker product) of two quantum gates is the gate that is equal to the two gates in parallel.
  If we, as in the picture, combine the Pauli-Y gate with the Pauli-X gate in parallel, then this can be written as: 
  Both the Pauli-X and the Pauli-Y gate act on a single qubit. The resulting gate  act on two qubits.
caption: Two gates 
    
      
        
          Y
        
      
      {\displaystyle Y}
    
   and 
    
      
        
          X
        
      
      {\displaystyle X}
    
   in parallel is equivalent to the gate 
    
      
        
          Y
          ⊗
          X
        
      
      {\displaystyle Y\otimes X}
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