MULT20015 20201QUI Intro
QUI Introduction, Ó L. Hollenberg et al 2020-2021 1
MULT20015 Elements to Quantum Computing
Introduction to the Quantum User Interface (QUI)
The QUI is a web-based graphical user interface to program, simulate and analyse quantum
circuits. It was developed by the Hollenberg group at the University of Melbourne. The QUI
allows the users to specify qubit number, build and simulate quantum circuits by easy
drag-and-drop placement of quantum gates, and examine the quantum state at every time
step in the circuit/program. The latter feature is critical to understanding QC, and
distinguishes the QUI from other on-line QC programing/simulation tools.
Sign up and start the QUI
The QUI is accessed through a web-based interface (quispace.org – click on blue QUI logo).
As per the subject announcement you should have signed up prior to the Lab-1 class – if
you haven’t please let a demonstrator know and follow these steps.
Step 1: Open a web browser (preferably Google Chrome or Firefox), go to quispace.org.
Step 2: You will need to create an account to access QUI for the first time.
Note: In order to access expanded capabilities of the QUI you must use your
University of Melbourne email address as your login name.
Follow the steps to create your account (including answering a few simple questions about
use and education level).
Step 3: Once you have signed-up, start the QUI.
The QUI panels
Shown below are the various QUI panels.
QUI Introduction, Ó L. Hollenberg et al 2020-2021 2
Editor (Panel 1): This is where a quantum circuit is programed by dragging and dropping
from the gate Library (Panel 2). On the left side, the initial states of three qubits (for this
example) are shown in the default |0⟩ state. You can add more qubits using the |*> icon
(or QUBITS in the Control panel). The vertical lines separate time steps left to right. The
thicker vertical with the left-right arrow is the “time-slider”, which can be moved to analyse
the quantum state at different times in the quantum circuit. The time-slider will also display
the degree of entanglement at various parts of the quantum circuit (Lab 2).
Library (Panel 2): This panel shows the gate library (quantum operations), including
measurement. Hovering the cursor over any single-qubit gate will display the animation of
the corresponding operation on the Bloch sphere. Select one of these gates and place it
in the Editor panel at the desired location(s). There is even a paint feature.
Control (Panel 3): The colour scales on the left side indicate the min-max range of
various output parameters (probability, entanglement, phase). Next is a drop-down FILE
menu (New, Save, Load, Save As). QUBITS allows the users to select the number of qubits.
DELETE removes selected quantum gates from the circuit. COMPUTE will run the current
circuit and display the results in the Inspector panel (more accurately, the circuit is sent
to our quantum simulator and the entire set of results (all time points) is sent back to
your QUI session for analysing – please don’t sit there and hit compute a million times).
Inspector (Panel 4): Here you can visualise the quantum state (after compute) at any
time point corresponding to the position of the sliding time-slider. By default, the horizontal
axis is ordered according to the state index in the computational basis (|11> = |3> etc),
and the vertical axis by default gives the probability of each state. Detailed information
about the state amplitudes (magnitude and phase) is given in the State Info Card that
pops up when the mouse hovers over a state in the histogram. Note the hazard warning
symbol bottom right – this indicates the current Inspector plot does not contain up-to-date
data (i.e. with respect to changes in the circuit shown in the Editor).
Settings (Panel 5): Here the user has additional control over the various plotting options
in the Inspector, such as PLOT RANGE, ORDERING, and AXIS (data) options.
State Info Card (Panel 6): This panel appears when the cursor is on a particular state
in the Inspector panel and will display all information about the state’s identity (binary and
integer index), complex valued amplitude (magnitude and phase), and probability.