- Any computer with a Web browser.

At the top is the pure state ** |0>**
and at the bottom is the pure state

`|1>`

Quantum computers use the whole range of states, including the
intermediate states that are "superpositions" of ** |0>** and

`|1>`

In a Web browser, go to

https://quantumexperience.ng.bluemix.net/qx/experience

Click the "**Start experimenting
with a quantum computer**"
button,
as shown below.

The next page shows the "Composer". Here we'll program a quantum computer, using the chart at the bottom with five lines, like a music composer's score.

At the top is the **Internals**
section, showing the details of
IBM's actual quantum computer.
Ignore it for this project.

At the lower left is the **Score**
where you will create your programs,
by dragging **Gates** from the right
and dropping them.

The pink icon with a white umbrella-looking
figure on it is called
a "**Measurement Gate**". Drag
a measurement gate onto the score
and drop it there, as indicated by the
pink arrow in the figure below.

At the center right, click the
**Simulate** button.

A login box pops up, as shown below. Log in with a social network, or create an IBM Q account and log in with that.

It puts you on a forum page. Refresh the page
to implement the log in. Then, from the top menu,
click **Learn**, **Composer**,
as shown below.

Drag the pink "**Measurement Gate**"
onto the score
and drop it there again.

Click the
**Simulate** button.

A box pops up asking you to "Name
your experiment". Click **OK**.

"Your Quantum Results" appear, including the "Quantum State: Computation Basis" chart shown below.

This chart shows the results of running
your experiment 100 times. Every time,
the result was the same: **00000**,
as shown at the bottom of the purple
bar.

It did not demonstrate any quantum behavior. There are five Qubits, and they all start in the "Zero" state, written as

All you did was measure one Qubit, and the result was always`|0>`

Click the
**Simulate** button.
You get the same result:
**00000** every time,
as shown in the upper part of the
image below.

This is how ordinary non-quantum processors work. Measuring a bit has no effect on it--you can measure it anytime you want.

Drag gates as needed to make the quantum
score shown below, and **Simulate**
it.

The green **X** gate flips a Qubit from
** |0>**
to

`|1>`

This is still the same as a normal processor: no quantum effects are visible.

Drag gates as needed to make the quantum
score shown below, and **Simulate**
it.

The blue **H** gate
is called a "Hadamard" gate, and it changes
a Qubit from its
** |0>**
state to a "Superposition" state,
mixing equal portions of the

`|0>`

`|1>`

This is also called "Uncertainty" and it's the bizarre part of quantum mechanics: quantum objects in a "Superposition" state are neither 1 nor 0, but in an uncertain state with a probability of either result.

So the measurement doesn't always give the same
result. Half the time the result is **00001**
and the other half of the time it's
**00000**.

Drag gates as needed to make the quantum
score shown below, and **Simulate**
it.

The three Qubits are all in Superposition states, so there are eight possible results with equal probability.

Drag gates as needed to make the quantum
score shown below, and **Simulate**
it.

The **H** gate makes the second Qubit
uncertain, but the other two Qubits are
stable in the
** |0>**
state,.

The only two possible answers are
**00000** and **00010**,
as shown below.

Drag gates as needed to make the quantum
score shown below, and **Simulate**
it.

The **+** gate **Entangles** two
Qubits, so they will always give the same
result when measured. So Qubit 0 now
follows Qubit 1, and the possible
results are now **00000** and
**00011**,
as shown below.

Drag gates as needed to make the quantum
score shown below, and **Simulate**
it.

Now Qubits 0 and 1 are entangled, but always
opposite,
so the possible
results are **00001** and
**00010**,
as shown below.

Combine all the bits of the possible answers to form the flag, like this:

```
0000011111
```

One of my students succeeded in entangling all five Qubits.

Show your instructor when you succeed. This challenge doesn't have a flag to enter into the automatic scoring engine.

Posted 1-3-18 by Sam Bowne

Added to Crypto Hero 4-16-18 8:45 am

Image added to make challenge possible 6-2-18

Background added 8-10-18

Login process updated 3-5-19

Ported to new scoring engine 7-8-19