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use rand;
use std::cell::Cell;
use gate::Gate;
use ket::Ket;
#[derive(Debug)]
pub struct QuantumRegister {
width: usize,
collapsed: Cell<bool>,
ket: Ket,
}
impl QuantumRegister {
pub fn new(width: usize, initial: &ClassicalRegister) -> QuantumRegister {
assert_eq!(width, initial.width());
QuantumRegister {
width: width,
collapsed: Cell::new(false),
ket: Ket::from_classical(initial),
}
}
pub fn apply(&mut self, gate: Gate) {
assert_eq!(false, self.collapsed.get());
assert_eq!(self.width, gate.width());
self.ket.apply(gate);
}
pub fn collapse(&mut self) -> ClassicalRegister {
assert_eq!(false, self.collapsed.get());
self.collapsed = Cell::new(true);
let sample = rand::random::<f64>() % 1.0;
let mut cumulative = 0f64;
for (state, coefficient) in self.ket.elements.iter().enumerate() {
cumulative += coefficient.norm_sqr();
if sample < cumulative {
return ClassicalRegister::from_state(self.width, state as u32);
}
}
ClassicalRegister::from_state(self.width, 0)
}
pub fn probabilities(&self) -> Vec<f64> {
assert_eq!(false, self.collapsed.get());
let mut probabilities = vec![];
for (_, coefficient) in self.ket.elements.iter().take(Ket::size(self.width)).enumerate() {
probabilities.push(coefficient.norm_sqr());
}
probabilities
}
}
#[test]
fn initialization_test() {
let nibble = ClassicalRegister::zeroed(4);
let r: QuantumRegister = QuantumRegister::new(4, &nibble);
assert_eq!(false, r.collapsed.get());
assert_eq!(4, r.width);
assert!(&r.ket.is_classical());
}
#[test]
fn collapse_test() {
let nibble = ClassicalRegister::zeroed(4);
let mut r: QuantumRegister = QuantumRegister::new(4, &nibble);
let end: ClassicalRegister = r.collapse();
assert_eq!(nibble, end);
assert!(r.collapsed.get());
}
#[test]
#[should_panic(expected = "assertion failed")]
fn double_collapse_test() {
let nibble = ClassicalRegister::zeroed(4);
let mut r: QuantumRegister = QuantumRegister::new(4, &nibble);
r.collapse();
r.collapse();
}
#[test]
fn probabilities_test() {
use float_cmp::ApproxEqUlps;
use gates;
let nibble = ClassicalRegister::zeroed(1);
let mut r: QuantumRegister = QuantumRegister::new(1, &nibble);
r.apply(gates::hadamard(1));
assert_eq!(2, r.probabilities().len());
assert!(0.5f64.approx_eq_ulps(&r.probabilities()[0], 10));
assert!(0.5f64.approx_eq_ulps(&r.probabilities()[1], 10));
}
#[derive(Debug, Eq, PartialEq)]
pub struct ClassicalRegister {
bits: Vec<u8>,
}
impl ClassicalRegister {
pub fn new(bits: Vec<u8>) -> ClassicalRegister {
for bit in &bits {
assert!(0 == *bit || 1 == *bit);
}
ClassicalRegister { bits: bits }
}
pub fn from_state(width: usize, state: u32) -> ClassicalRegister {
assert!(state < 2u32.pow(width as u32));
let mut bits = Vec::new();
let mut remaining_state = state;
for i in 0..width {
let pos: u32 = (width - i - 1) as u32;
let value = 2u32.pow(pos);
if value <= remaining_state {
remaining_state -= value;
bits.insert(0, 1);
} else {
bits.insert(0, 0);
}
}
ClassicalRegister::new(bits)
}
pub fn from_int(width: usize, int: u32) -> ClassicalRegister {
ClassicalRegister::from_state(width, int)
}
pub fn zeroed(width: usize) -> ClassicalRegister {
ClassicalRegister::new(vec![0; width])
}
pub fn width(&self) -> usize {
self.bits.len()
}
pub fn state(&self) -> u32 {
let mut state = 0u32;
for (pos, bit) in self.bits.iter().enumerate() {
if 0u8 != *bit {
state += 2u32.pow(pos as u32);
}
}
state
}
pub fn to_int(&self) -> u32 {
self.state()
}
}
#[test]
fn state_test() {
let nibble = ClassicalRegister::new(vec![0, 1, 0, 1]);
assert_eq!(10, nibble.state());
assert_eq!(nibble, ClassicalRegister::from_state(4, nibble.state()));
}