Dark Magic Operations

Warning

The operations in this section bypass the normal constraints of quantum mechanics and are not guaranteed to be unitary. Use them only for debugging, initialization, or when you clearly understand the consequences.

Dark magic operations provide the ability to directly modify the internal representation of a quantum state without going through normal quantum gate transformations. These operations do not correspond to any physical quantum operations.

Overview

Dark magic operations overview

Operator	Operation	Unitarity
Normalize	Normalize the quantum state	Non-unitary
Init_Unsafe	Set a register value directly	Non-unitary

—

Normalize

Operation: Normalizes the amplitudes of the entire SparseState so that \(\sum_i |\alpha_i|^2 = 1\).

Parameters: None.

Purpose: Use this operator to repair a quantum state that has been left unnormalized by manual manipulation (e.g. Init_Unsafe) or by numerical error.

import pysparq as ps

# Suppose some operations have left the quantum state unnormalized
ps.Normalize()(state)

# You can check it with ViewNormalization
ps.ViewNormalization()(state)

—

Init_Unsafe (unsafe initialization)

Operation: Directly sets the value of the specified register to a given constant, without going through any quantum gate.

Parameters:

• reg — target register (name or ID)

• value — the value to set (integer)

Behavior: Iterates over all basis states and forcibly sets the specified register’s value to value. If multiple basis states end up with duplicate keys after the assignment, their amplitudes are summed.

Warning

This operation is not guaranteed to be unitary. It destroys superposition information — if the register was in a superposition, all components other than value are overwritten.

import pysparq as ps

ps.System.clear()
ps.System.add_register("a", ps.UnsignedInteger, 4)
ps.System.add_register("b", ps.UnsignedInteger, 4)

state = ps.SparseState()

# Set the initial values directly
ps.Init_Unsafe("a", 3)(state)
ps.Init_Unsafe("b", 5)(state)

ps.pprint(state)
# |a=3,b=5⟩ : (1+0j)

Note

The most common use of Init_Unsafe is to set the initial values of the input registers at the start of an algorithm. Be especially careful when using it on a superposed state.