`q1tsim`

The quantum simulation library `q1tsim`

has seen a lot of
development since its initial release. New features that are available include:

- A few new gate types, allowing for simpler circuit descriptions.
- The ability to simulate measurements without disrupting the quantum state. This allows one to continue simulations with the state before the measurement.
- The option to re-run a circuit starting with the previous quantum state.
- A new stabilizer backend, allowing for the simulation of pure stabilizer circuits with thousands of qubits.

Most recently, a Python interface has been added to the library, allowing
one to easily use most of the `q1tsim`

features from Python. The
newest release is available on
Github,
both as source code or as a directly usable binary packages for
Windows and Linux.

Building upon our previous work on modelling quantum optical problems
on a quantum computer, we turned our attention to a more involved problem:
simulating an actual quantum optical interference experiment.
In the experiment
[Eschner et al., Nature 431, 495 (2001)],
a single Ba^{+} ion was held in a Paul trap in front of a mirror.
The ion was excited using a laser, and it was shown by varying the distance of the ion to mirror, that the subsequent fluorescence emitted by the ion interfered
with its mirror image.

We were able to model this setup, which involves a fully coherent feedback loop,
in terms of a quantum circuit, that we simulated on our `q1tsim`

simulator. By reusing qubits in the simulation, the circuit
required no more than six qubits to succesfully reproduce
the interference pattern that was observed experimentally. Furthermore,
we were able to show the effect of the back-reflected light as a function
of the ion-mirror distance on the emission rate of the ion itself.

Given the limited number of qubits required, we believe the circuits we present are ready to be implemented on actual state-of-the-art quantum computers that are able to re-initialize qubits.

Read the published paper or the preprint on the ArXiv.

`q1tsim`

is a Rust library for simulating a (perfect)
quantum computer. It aims to be an easy to use, efficient simulator for the
development and testing of quantum algorithms. Features of `q1tsim`

include:
- Easy implementation and simulation of quantum circuits
- Supports the creation of arbitrary quantum gates
- Most common quantum gates already included
- Measurement in
*X*,*Y*, or*Z*basis - Creation of histograms of measurement results over multiple runs
- Operations conditional on classical values
- Export of circuits to Open QASM and c-QASM

`q1tsim`

package on
crates.io,
or view the development tree on
Github.
Quantum optics is a very fruitful field of study for quantum computers. It is well known how to discretize the problems that arise in this field, and the resulting quantum stochastic difference equations are easily mapped to quantum computer instructions. This, combined with the fact that there are many interesting problems and techniques in quantum optics, makes it an eminently suitable field for benchmarking early quantum computers.

On the other hand, using a quantum computer one can do fully coherent simulations of a system in an electromagnetic field, something that is only possible up to a certain point in classical computers. We are no longer limited to just observing the effect of the electromagnetic field on the atom, but can also provide a full description of the field itself. This way, the use of quantum computers may help further our understanding of quantum optics.

We started our experiments with a study of a laser driven two-level atom in interaction with the vacuum electromagnetic field. We used the publically accessible IBMqx4 Tenerife quantum computer to simulate the evolution of the state of this atom, and compared the results to the dynamics given by the theoretical master equation. Furthermore, we computed the conditional dynamics of the atom on both counting photons in the field and observing a field quadrature in the field, and compared the results to those predicted by the relevant quantum filtering equations.

Read the published paper, or the preprint on the ArXiv.

Download our poster for the 2019 EQTC conference in Grenoble.

Lindenlaan 15

6584 AC Molenhoek

The Netherlands

invoice@q1t.nl