Intro to Qc on Strathweb. A free flowing tech monologue.

Introduction to quantum computing with Q# – Part 19, Quantum Phase Estimation

Wed, 28 Apr 2021 14:20:56 +0000

Last time we discussed the Quantum Fourier Transform - one of the important building blocks for more complex quantum algorithms. In this post, we will build upon that knowledge and take advantage of the QFT functionality, to explore another important subroutine that is used in many quantum programs, namely quantum phase estimation.

Introduction to quantum computing with Q# – Part 18, Quantum Fourier Transform

Thu, 01 Apr 2021 06:56:54 +0000

In today’s post we will explore one of the important algorithm building blocks in quantum computing theory, called the Quantum Fourier Transform. It is a quantum variant of the classical Discrete Fourier Transform and is used in a number of algorithms such as Shor’s factoring algorithm, quantum phase estimation or quantum algorithm for linear systems of equations.

Introduction to quantum computing with Q# – Part 17, Grover’s algorithm

Fri, 19 Mar 2021 15:49:31 +0000

Last time we looked at the basic theory behind quantum search based on the Grover’s algorithm. We went through the most basic case, a data set consisting of four items, and applied the algorithm to that, learning in the process that it managed to find the relevant entry we were looking for in a single step - compared to an average expected 2.25 steps required by the classical computation theory.

In this part, we will look at the more general theory behind Grover’s algorithm, and implement the general Q# variant that can be used to find any number in an arbitrarily large data set.

Introduction to quantum computing with Q# – Part 16, Quantum search

Fri, 05 Mar 2021 21:08:31 +0000

In this post we will start exploring the topic of quantum search - the ability to locate a specific qubit state in an unsorted data set represented in a qubit register. We will look at the mathematics behind this problem, at the Q# code illustrating some basic examples and explain how the different building blocks fit together. This will help us lay ground for a more comprehensive discussion of the so-called Grover’s algorithm next time.

Introduction to quantum computing with Q# – Part 15, Deutsch-Jozsa algorithm

Thu, 25 Feb 2021 08:25:20 +0000

Last time, we discussed a problem originally stated by David Deutsch, focusing on determining whether a function is constant or balanced. We found out that for that specific problem, quantum computing provides a much better query complexity than classical computing - as it can solve the task in a single blackbox function evaluation, while classical computing requires two function evaluations to provide the same answer.

Today, we shall look at the generalization of that simple problem.

Introduction to quantum computing with Q# – Part 14, Deutsch’s problem

Mon, 18 Jan 2021 20:08:22 +0000

Over the course of this series, we have developed a solid foundational understanding of quantum computing, as we learned about the basic paradigms, mathematics and various computational concepts that characterize this unique disciple. We are now well equipped to start exploring some of the most important quantum algorithms - starting with today’s part 14, which will be devoted to a simple oracle problem formulated by David Deutsch.

Introduction to quantum computing with Q# – Part 13, CHSH Game

Wed, 06 Jan 2021 21:43:21 +0000

Last time we had an in-depth look at the original Bell’s inequality, and we wrote some Q# code that allowed us to quickly empirically test the predictions of quantum mechanics in that area.

In today’s post, we will continue with a generalization of Bell’s inequalities, called Clauser-Horne-Shimony-Holt
inequality (in short CHSH), and discuss a simple game based on that. In the process, we will arrive at a remarkable conclusions - we will learn that for a certain class of simple boolean logic problems, they can be solved more efficiently when adopting a quantum strategy compared to a classical “common sense” approach.

Introduction to quantum computing with Q# – Part 12, Bell’s inequality

Tue, 22 Dec 2020 14:33:50 +0000

After a short multi-part detour into the world of quantum cryptography, in this part 12 of the series, we are going to return to some of the foundational concepts of quantum mechanics, and look at the programmatic verification of Bell’s inequality.

Introduction to quantum computing with Q# – Part 11, EPR Quantum Key Distribution

Wed, 02 Dec 2020 22:24:49 +0000

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.

Introduction to quantum computing with Q# – Part 10, B92 Quantum Key Distribution

Tue, 17 Nov 2020 20:50:49 +0000

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.

Introduction to quantum computing with Q# – Part 9, BB84 Quantum Key Distribution

Fri, 16 Oct 2020 12:54:26 +0000

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#.

Introduction to quantum computing with Q# – Part 8, Superdense coding

Wed, 16 Sep 2020 18:25:15 +0000

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 communicating two classical bits of information between two parties, by moving only a single qubit between them.

Introduction to quantum computing with Q# – Part 7, Quantum state teleportation

Fri, 04 Sep 2020 04:50:56 +0000

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.

Introduction to quantum computing with Q# – Part 6, No-cloning theorem

Mon, 17 Aug 2020 20:54:58 +0000

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?

Introduction to quantum computing with Q# – Part 5, Entanglement

Mon, 06 Jul 2020 13:15:50 +0000

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.

Introduction to quantum computing with Q# – Part 4, multi-qubit gates

Wed, 24 Jun 2020 18:07:08 +0000

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.

Introduction to quantum computing with Q# – Part 3, Single qubit gates

Wed, 20 May 2020 05:50:20 +0000

We left off in the last post after having discussed the Hadamard gate - our first quantum gate - and how it can be used to crate a uniform superposiiton for a single qubit. We are going to continue today by exploring other single qubit gates, discussing the underlying mathematics and, of course, testing it all out with some Q# code.

Introduction to quantum computing with Q# – Part 2, Superposition

Wed, 08 Apr 2020 19:52:34 +0000

In the previous post in this series we mentioned the concept of superposition briefly. Let’s use this second part to dive deeper into the mathematics of it, meet the cat of Schrödinger and try to find some simple quantum computing use cases for it.

Introduction to quantum computing with Q# – Part 1, The background and the qubit

Fri, 20 Mar 2020 15:12:40 +0000

Quantum mechanics is one of the fundamental theories of physics, and has been tremendously successful at describing the behavior of subatomic particles. However, its counter-intuitive probabilistic nature, bizarre rules and confusing epistemology have troubled some of the greatest physicists of the 20th century, even prompting Albert Einstein to remark “Old Man (often translated as ‘God’) doesn’t play dice”.

In this post I am starting a new series that will introduce the basics of quantum computing - using examples in Q#.