Quantum Computing library leveraging graph building to build efficient quantum circuit simulations. Rust is a great language for quantum computing with gate models because the borrow checker is very similar to the No-cloning theorem.

See all the examples in the examples directory of the Github repository.

Example (CSWAP)

Here's an example of a small circuit where two groups of Registers are swapped conditioned on a third. This circuit is very small, only three operations plus a measurement, so the boilerplate can look quite large in comparison, but that setup provides the ability to construct circuits easily and safely when they do get larger.

use qip::prelude::*;
use std::num::NonZeroUsize;

// Make a new circuit builder.
let mut b = LocalBuilder::<f64>::default();
let n = NonZeroUsize::new(3).unwrap();

// Make three registers of sizes 1, 3, 3 (7 qubits total).
let q = b.qubit();  // Same as b.register(1)?;
let ra = b.register(n);
let rb = b.register(n);

// Define circuit
// First apply an H to q
let q = b.h(q);
// Then swap ra and rb, conditioned on q.
let mut cb = b.condition_with(q);
let (ra, rb) = cb.swap(ra, rb)?;
let q = cb.dissolve();
// Finally apply H to q again.
let q = b.h(q);

// Add a measurement to the first qubit, save a reference so we can get the result later.
let (q, m_handle) = b.measure(q);

// Now q is the end result of the above circuit, and we can run the circuit by referencing it.

// Run circuit with a given precision.
let (_, measured) = b.calculate_state_with_init([(&ra, 0b000), (&rb, 0b001)]);

// Lookup the result of the measurement we performed using the handle, and the probability
// of getting that measurement.
let (result, p) = measured.get_measurement(m_handle);

// Print the measured result
println!("Measured: {:?} (with chance {:?})", result, p);

The Program Macro

While the borrow checker included in rust is a wonderful tool for checking that our registers are behaving, it can be cumbersome. For that reason qip also includes a macro which provides an API similar to that which you would see in quantum computing textbooks.

use qip::prelude::*;
use std::num::NonZeroUsize;
use qip_macros::program;

fn gamma<B>(b: &mut B, ra: B::Register, rb: B::Register) -> CircuitResult<(B::Register, B::Register)>
   where B: AdvancedCircuitBuilder<f64>
{
    let (ra, rb) = b.toffoli(ra, rb)?;
    let (rb, ra) = b.toffoli(rb, ra)?;
    Ok((ra, rb))
}

let n = NonZeroUsize::new(3).unwrap();
let mut b = LocalBuilder::default();
let ra = b.register(n);
let rb = b.register(n);


let (ra, rb) = program!(&mut b; ra, rb;
    // Applies gamma to |ra[0] ra[1]>|ra[2]>
    gamma ra[0..2], ra[2];
    // Applies gamma to |ra[0] rb[0]>|ra[2]>
    // Notice ra[0] and rb[0] are grouped by brackets.
    gamma [ra[0], rb[0]], ra[2];
    // Applies gamma to |ra[0]>|rb[0] ra[2]>
    gamma ra[0], [rb[0], ra[2]];
    // Applies gamma to |ra[0] ra[1]>|ra[2]> if rb == |111>
    control gamma rb, ra[0..2], ra[2];
    // Applies gamma to |ra[0] ra[1]>|ra[2]> if rb == |110> (rb[0] == |0>, rb[1] == 1, ...)
    control(0b110) gamma rb, ra[0..2], ra[2];
)?;
let r = b.merge_two_registers(ra, rb);

We can also apply this to function which take other argument. Here gamma takes a boolean argument skip which is passed in before the registers. The arguments to functions in the program macro may not reference the input registers

use qip::prelude::*;
use std::num::NonZeroUsize;
use qip_macros::program;

fn gamma<B>(b: &mut B, skip: bool, ra: B::Register, rb: B::Register) -> CircuitResult<(B::Register, B::Register)>
   where B: AdvancedCircuitBuilder<f64>
{
    let (ra, rb) = b.toffoli(ra, rb)?;
    let (rb, ra) = if skip {
        b.toffoli(rb, ra)?
    } else {
        (rb, ra)
    };
    Ok((ra, rb))
}

let n = NonZeroUsize::new(3).unwrap();
let mut b = LocalBuilder::default();
let ra = b.register(n);
let rb = b.register(n);

let (ra, rb) = program!(&mut b; ra, rb;
    gamma(true) ra[0..2], ra[2];
    gamma(0 == 1) ra[0..2], ra[2];
)?;
let r = b.merge_two_registers(ra, rb);

The Invert Macro

It's often useful to define functions of registers as well as their inverses, the #[invert] macro automates much of this process.

use qip::prelude::*;
use std::num::NonZeroUsize;
use qip_macros::*;

use qip::inverter::Invertable;
// Make gamma and its inverse: gamma_inv
#[invert(gamma_inv)]
fn gamma<B>(b: &mut B, ra: B::Register, rb: B::Register) -> CircuitResult<(B::Register, B::Register)>
   where B: AdvancedCircuitBuilder<f64> + Invertable<SimilarBuilder=B>
{
    let (ra, rb) = b.toffoli(ra, rb)?;
    let (rb, ra) = b.toffoli(rb, ra)?;
    Ok((ra, rb))
}

let n = NonZeroUsize::new(3).unwrap();
let mut b = LocalBuilder::default();
let ra = b.register(n);
let rb = b.register(n);


let (ra, rb) = program!(&mut b; ra, rb;
    gamma ra[0..2], ra[2];
    gamma_inv ra[0..2], ra[2];
)?;
let r = b.merge_two_registers(ra, rb);

To invert functions with additional arguments, we must list the non-register arguments.

use qip::prelude::*;
use std::num::NonZeroUsize;
use qip_macros::*;

use qip::inverter::Invertable;
// Make gamma and its inverse: gamma_inv
#[invert(gamma_inv, skip)]
fn gamma<B>(b: &mut B, skip: bool, ra: B::Register, rb: B::Register) -> CircuitResult<(B::Register, B::Register)>
   where B: AdvancedCircuitBuilder<f64> + Invertable<SimilarBuilder=B>
{
    let (ra, rb) = b.toffoli(ra, rb)?;
    let (rb, ra) = if skip {
        b.toffoli(rb, ra)?
    } else {
        (rb, ra)
    };
    Ok((ra, rb))
}

let n = NonZeroUsize::new(3).unwrap();
let mut b = LocalBuilder::default();
let ra = b.register(n);
let rb = b.register(n);

let (ra, rb) = program!(&mut b; ra, rb;
    gamma(true) ra[0..2], ra[2];
    gamma_inv(true) ra[0..2], ra[2];
)?;
let r = b.merge_two_registers(ra, rb);