Class: State

Inherits:
Object
  • Object
show all
Includes:
QuantumVector
Defined in:
lib/quantum_ruby.rb

Overview

The State class represents a combination of qubits’ superpositions. They are stored a 2**n-dimensional column vector where N is the numbers of qubits entangled. State is usually produce after the applications of gates to a number of qubits and is continually passed forward through the quantum circuit until a measurement is made. State can be operated on via matrix multiplication or measurement(partial or otherwise).

Constant Summary

Constants included from QuantumVector

QuantumVector::PRECISION

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from QuantumVector

#==, #state

Constructor Details

#initialize(vector, *qubits) ⇒ State

Takes a column matrix representing N qubits and the corresponding superposition Values of the matrix must obey the normalization constraint Additional takes references to the actual qubits so that they can be updated in the future



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# File 'lib/quantum_ruby.rb', line 206

def initialize(vector, *qubits)
  @vector = vector
  column_vector?
  normalized?

  @qubits = qubits.flatten.tap { |i| i.each { |j| j.entangled = true } }
end

Instance Attribute Details

#qubits ⇒ Object (readonly)

Returns the value of attribute qubits.



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# File 'lib/quantum_ruby.rb', line 199

def qubits
  @qubits
end

#vector ⇒ Object (readonly)

Returns the value of attribute vector.



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# File 'lib/quantum_ruby.rb', line 198

def vector
  @vector
end

Instance Method Details

#measure ⇒ Object

Returns an array of bits representing the final state of all entangled qubits All qubits are written with their new state and all superposition information is lost



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# File 'lib/quantum_ruby.rb', line 217

def measure
  measure_partial(@qubits)
end

#measure_partial(*qubit) ⇒ Object

Takes an array of qubits for which a measurement should be made Returns an array of bits representing the final state of the requested qubits All others qubits are written with a normalized state and all superposition information is lost



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# File 'lib/quantum_ruby.rb', line 225

def measure_partial(*qubit)
  # find location of our desired qubit(s)
  qubit_ids = qubit.map { |i| @qubits.find_index { |j| j.hash == i .hash } }.sort

  # collect probabilities for qubit(s) states
  sub_result = @vector.to_a.flatten.each_with_index.group_by do |_probability, index|
    qubit_ids.map do |id|
      index.to_s(2).rjust(size, '0')[id]
    end.join
  end

  # calculate final probabilities for qubit(s) state
  probabilities = sub_result.sort.to_h.transform_values { |v| v.reduce(0) { |i, p| i + p[0].abs2 } }.values

  # determine 'winner'
  acc = 0
  out = nil
  secret = rand
  probabilities.each_with_index do |probability, index|
    acc += probability
    if acc > secret
      out = index
      break
    end
  end

  # Renormalize
  squared_sum_mag = Math.sqrt(probabilities[out])
  out = out.to_s(2).rjust(qubit.length, '0')
  new_state = sub_result.fetch(out).map { |i| i[0] / squared_sum_mag }

  # Update each qubit
  @qubits.each_with_index do |q, i|
    q.entangled = false
    if (index = qubit_ids.find_index(i))
      q.send(:vector=, Array.new(2, 0).tap { |vector| vector[out[index].to_i] = 1 })
    else
      q.send(:vector=, new_state)
    end
  end

  # State should no longer be used
  out.split('').map(&:to_i)
end