In the last two posts we covered quantum key exchange using the B92 and BB84 protocols. Both of those depended with their security on the no-cloning theorem. Today we are going to dedicate a third post to the topic of quantum key distribution, and this time around we will explore a variant of key distribution relying on the phenomenon of entanglement and quantum correlations.
In the last part of this series we started talking about the area of quantum cryptography, or more accurately, quantum key distribution. We dissected, in considerable amount of detail, the BB84 protocol, and discussed how it can lead to effectively unbreakable cryptography.
Today we shall continue with quantum key distribution by looking at a sibling to BB84, the B92 protocol.
This is already part 9 of the series (time flies!). So far we have covered a wide array of topic around the nature of quantum computational units called qubits, superposition, entanglement, single-qubit gates, multi-qubit gates and some interesting concepts from the area of quantum information theory. In this post we will shift our attention to another interesting field in the quantum landscape – quantum cryptography. More specifically, we will explore a reference protocol for quantum key distribution, called BB884, discuss why it’s secure even when using a public channel to exchange qubits and realize a simple demonstrative implementation using Q#.
Last time, we discussed the quantum teleportation protocol, which relies on the phenomenon of quantum entanglement to move an arbitrary quantum state from one qubit to another, even if they are spatially separated. Today, we shall continue exploring the scenarios enabled by entanglement, by looking at the concept called “superdense coding”. It allows sending two classical bits of information by physically moving only a single qubit around, and is sometimes referred to as a conceptual inverse of teleportation.
In the previous part of the series we discussed how quantum theory prohibits copying of an arbitrary quantum state. In computing terms, this means that regardless of the richness of features provided by high-level quantum-specific languages such as Q#, we cannot implement a classical functionality of copy-and-paste on a quantum computer.
It turns out, however, that we can achieve a cut-and-paste type of effect, through a remarkable process of quantum teleportation.
In the last part of this series we looked at the phenomenon of entanglement – one of the core concepts of quantum theory, which has been fundamentally important in the development of quantum information theory. We grappled with its deeply mysterious behavior and tried to understand and project its consequences onto the Q# code.
In today’s part 6, we shall ask ourselves a seemingly innocent question – how to you clone a quantum state, or in other words, how do you copy a qubit?
The QDK provides an excellent, low barrier way of getting started with Q# development – without having to deal with the compiler directly, or worrying about how to simulate the code you wrote on a classical device. Additionally, for more technically versed users, the Q# compiler is also available as a command line utility that can be used to fine tune the compilation experience and cater to complex scenarios. The QDK is well documented, and the command line compiler provides good documentation as part of the application itself, but one of the things that is not widely known is that the Q# compiler can also be easily used programmatically – via its Nuget package.
Let’s have a look.
In the last post in this series we dove deep into the mathematics and usage examples of multi-qubit gates, with special attention paid to one of the most critical gates in quantum computing, the CNOT gate.
In today’s post we are going to explore the wonders of entanglement – a core concept of quantum mechanics and a critical idea for quantum computing, where it is obtained via the application of the CNOT gate.
In the previous post of this series, we discussed single qubit gates. In this next instalment, we are going to explore gates that act on multiple qubits at once, thus completing the exploration of quantum circuit building. We are also going to slowly, but diligently uncover the underlying theoretical scheme towards one of the most bizarre concepts in quantum mechanics – entanglement, which is something that will be dedicating the next part to.
Last week I wrote a guest post on the Q# community blog about the new standalone/self-contained Q# applications that were introduced in Microsoft Quantum Development Kit 0.11.2004.2825.
In the post I go over the various aspects of the feature, discuss the new @EntryPoint() attribute that was introduced into Q# and dive deeper into some implementation details. Enjoy the article!