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Gates

All gate methods are chained directly on a QBitProxy returned by a qubit selector.

Single-Qubit Gates​

Q.bit(0).h()      // Hadamard
Q.bit(0).x()      // Pauli-X (NOT)
Q.bit(0).y()      // Pauli-Y
Q.bit(0).z()      // Pauli-Z
Q.bit(0).s()      // S gate (√Z)
Q.bit(0).s_()     // S† (S conjugate / SDG)
Q.bit(0).t()      // T gate (⁴√Z)
Q.bit(0).t_()     // T† (T conjugate / TDG)
Q.bit(0).id()     // Identity
Q.bit(0).reset()  // Reset to |0⟩

Rotation Gate​

The u() gate applies a general single-qubit unitary with three Euler angles [θ, φ, λ]:

Q.bit(0).u([0.3, 0.2, 0.1]); // U(θ=0.3, φ=0.2, λ=0.1)

Parameters can be numbers or AST expression objects (e.g. Q.π.div(2)).

Two-Qubit Gates​

Controlled gates take a target QBitProxy as argument:

Q.bit(0).cx(Q.bit(1))   // CNOT (alias: cnot)
Q.bit(0).cy(Q.bit(1))   // Controlled-Y
Q.bit(0).cz(Q.bit(1))   // Controlled-Z
Q.bit(0).ch(Q.bit(1))   // Controlled-Hadamard
Q.bit(0).swap(Q.bit(1)) // SWAP

Controlled Phase​

import { circuit } from '@quantum-js/dsl';

circuit({ qubits: 2 }, Q => {
  Q.bit(0).cp(Q.bit(1), Q.π.div(2)); // CP with θ = π/2
  Q.bit(0).cu1(Q.bit(1), 0.5);       // alias for cp
});

cp and cu1 are identical — cu1 is provided as an alias for compatibility with older circuit descriptions.

Three-Qubit Gate (Toffoli)​

Q.bit(0).ccx(Q.bit(1), Q.bit(2))      // Toffoli / CCX
Q.bit(0).toffoli(Q.bit(1), Q.bit(2))  // alias for ccx

Repeating a Gate​

Use .repeat() to apply the same gate multiple times:

Q.bit(0).repeat(3, 'h'); // Apply H three times

π Expressions​

For parameterized gates, QuantumJS provides a symbolic π helper to keep QASM output clean:

Q.π.div(2)   // π/2
Q.π.div(4)   // π/4

// Or using the standalone helpers:
import { pi, div } from '@quantum-js/dsl';
div(pi, 2)   // π/2

These produce symbolic AST expressions that emit as (pi / 2) in QASM rather than a floating-point approximation.