| title | description | author | ms.author | ms.date | ms.topic | uid |
|---|---|---|---|---|---|---|
Create a Quantum Random Number Generator |
Build a Q# project that demonstrates fundamental quantum concepts like superposition by creating a quantum random number generator. |
bromeg |
megbrow@microsoft.com |
10/25/2019 |
article |
microsoft.quantum.quickstarts.qrng |
A simple example of a quantum algorithm written in Q# is a quantum random number generator. This algorithm leverages the nature of quantum mechanics to produce a random number.
- The Microsoft Quantum Development Kit.
- Create a Q# Project
- Replace the contents of the Program.qs file with the following code:
:::code language="qsharp" source="~/quantum/samples/getting-started/qrng/Qrng.qs" range="3-15,34":::
As mentioned in our What is Quantum Computing? article, a qubit is a unit of quantum information that can be in superposition. When measured, a qubit can only be either 0 or 1. However, during execution the state of the qubit represents the probability of reading either a 0 or a 1 with a measurement. This probabilistic state is known as superposition. We can use this probability to generate random numbers.
In our Q# operation, we introduce the Qubit datatype, native to Q#. We can only allocate a Qubit with a using statement. When it gets allocated, a qubit is always in the Zero state.
Using the H operation, we are able to put our Qubit in superposition. To measure a qubit and read its value, you use the M intrinsic operation.
By putting our Qubit in superposition and measuring it, our result will be a different value each time the code is invoked.
When a Qubit is de-allocated it must be explicitly set back to the Zero state, otherwise the simulator will report a runtime error. An easy way to achieve this is invoking Reset.
In the Bloch sphere, the north pole represents the classical value 0 and the south pole represents the classical value 1. Any superposition can be represented by a point on the sphere (represented by an arrow). The closer the end of the arrow to a pole the higher the probability the qubit collapses into the classical value assigned to that pole when measured. For example, the qubit state represented by the red arrow below has a higher probability of giving the value 0 if we measure it.
We can use this representation to visualize what the code is doing:
- First we start with a qubit initialized in the state 0 and apply
Hto create a superposition in which the probabilities for 0 and 1 are the same.
- Then we measure the qubit and save the output:
Since the outcome of the measurement is completely random, we have obtained a random bit. We can call this operation several times to create integers. For example, if we call the operation three times to obtain three random bits, we can build random 3-bit numbers (that is, a random number between 0 and 7).
Now that we have a Q# operation that generates random bits, we can use it to build a complete quantum random number generator. We can use the Q# command line applications or use a host program.
To create the full Q# command line application, add the following entry point to your Q# program:
:::code language="qsharp" source="~/quantum/samples/getting-started/qrng/Qrng.qs" range="17-33":::
The executable will run the operation or function marked with the @EntryPoint() attribute on a simulator or resource estimator, depending on the project configuration and command-line options.
:::code language="qsharp" source="~/quantum/samples/getting-started/qrng/Qrng.qs" range="3-34":::
In Visual Studio, simply press Ctrl + F5 to execute the script.
In VS Code, build the Program.qs the first time by typing the below in the terminal:
dotnet build
For subsequent runs, there is no need to build it again. To run it, type the following command and press enter:
dotnet run --no-build
To run your new Q# program from Python, save the following code as host.py:
:::code language="python" source="~/quantum/samples/interoperability/qrng/host.py" range="11-30":::
You can then run your Python host program from the command line:
$ python host.py
Preparing Q# environment...
..The random number generated is 42To run your new Q# program from C#, modify Driver.cs to include the following C# code:
:::code language="csharp" source="~/quantum/samples/interoperability/qrng/Host.cs" range="4-39":::
You can then run your C# host program from the command line (in Visual Studio you should press F5):
$ dotnet run
The random number generated is 42