In summary: No computer needed; it's called a chastity belt (or sterilization if you are a 'belt & suspenders' type of guy)....
Bob Walance
Gold Member
TL;DR Summary
A document, for beginners, describing how quantum computers work with comparisons to conventional computers.

#### Attachments

• An Introduction to Quantum Computing.pdf
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Quantum Panda, iamanegg, WWGD and 10 others
There are some tutorials on https://quantum-computing.ibm.com/docs/ which may be useful.

This might also be useful: https://dl.acm.org/doi/10.1145/3517340
Quantum Algorithm Implementations for Beginners
"We survey 20 different quantum algorithms, attempting to describe each in a succinct and self-contained fashion. We show how these algorithms can be implemented on IBM’s quantum computer, and in each case, we discuss the results of the implementation with respect to differences between the simulator and the actual hardware runs."

Code is available at : https://github.com/lanl/quantum_algorithms

aaroman, berkeman, vanhees71 and 2 others
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iamanegg, Delta2 and berkeman
Great idea for a new thread. I had a question that never got answered. It has to do with programming quantum computers.

If I have an algorithm S (Shor's Algorithm), how do I interconnect the qubits to implement it?

anorlunda said:
If I have an algorithm S (Shor's Algorithm), how do I interconnect the qubits to implement it?
You implement a classical control to orchestrate to required direct interactions between your qubits. The physical layout of your qubits determines which qubits can directly interact with each other, given the right classical control signal.

Such control signals could be microwave pulses of the right frequency and duration, or electrical wires put on the right potential, or a combination of both. Or it could be laser pulses, or modulations of a magnetic field, or other classically controllable phenomena.

anorlunda
anorlunda said:
If I have an algorithm S (Shor's Algorithm), how do I interconnect the qubits to implement it?
Shor's algorithm is fairly complex. In the quantum realm you need to do modular exponentiation and also the Fourier transform. In this thread (post #2), atyy shared a link to some code on github that will factor '15' but with a fixed initial guess. It's tough to factor bigger numbers and be more flexible on the initial guess because it takes 3x qubits to do the job and simulators are very limited due to current memory size.
I gave up implementing Shor's on the simulator that I wrote because with my 13 qubits max I could only hope to factor the number '15', too. It didn't seem worth the effort. We need faster processors and exabytes of ram to make it interesting (imo), or we can just wait for real quantum computers with a couple hundred error-corrected qubits .

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berkeman and anorlunda
Excellent!

Would this be useful to add to PF Insights? @Bob Walance?

berkeman and malawi_glenn
Greg Bernhardt said:
Would this be useful to add to PF Insights? @Bob Walance?
Greg - That's certainly okay with me. If you do that then, if you can, please use the attached updated pdf. There were a couple of spelling errors in the first draft (thanks to Tom.G for helping me out on this). There is now a 'r2' in the footnotes.

#### Attachments

• Introduction to quantum computing.pdf
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Tom.G, gentzen, Greg Bernhardt and 1 other person
I love the challenge to learn offered by this thread. Thank you @Bob Walance .I'm working my way carefully through Quantum Algorithm Implementations for Beginners linked in #2. I

I'm stuck on the notation in equation 11, page 18:5. I presume that the summation is for all possible values of X2 and X3, but I don't see how the notation says that.

PhDeezNutz
##\left(x_2x_3\right)\in\{0,1\}^2## just means that the string ##x_2x_3## is from the set of all 2-tuples of numbers belonging to ##\{0,1\}##. The notation is similar to how you would use ##R^n## for a coordinate space, just replace ##R## with ##\{0,1\}## and n with 2.
Then, as you presumed, the "bra" vectors in the sum will be ##\langle0\mathbf{00}|, \langle0\mathbf{01}|, \langle0\mathbf{10}|, \langle0\mathbf{11}|##.

malawi_glenn and anorlunda
Bob Walance said:
Summary: A document, for beginners, describing how quantum computers work with comparisons to conventional computers.

revisions for the attached PDF:
r3 - Changed all occurrences of the word 'conventional' to 'classical'. Headings are no longer all capital letters.
r2 - Fixed a couple of spelling and grammar errors.
Fun article. Thanks. How do I get access to a computer which will answer the question "what is the best possible method for getting humans to conceive only one child or less?" Thanks.

Photonics and Motore
Rich Thomasy said:
How do I get access to a computer which will answer the question "what is the best possible method for getting humans to conceive only one child or less?"

No computer needed; it's called a chastity belt (or sterilization if you are a 'belt & suspenders' type of guy).

Tom.G said:
No computer needed; it's called a chastity belt (or sterilization if you are a 'belt & suspenders' type of guy).
Fun reply. However, I was being serious.

"Quantum computation and quantum Information" by Nielsen e Chuang.
Ssnow

I have updated the PDF (now rev 4) with a few clarifications and corrections. Also, a table of contents has been added.

vanhees71, Greg Bernhardt and berkeman

## 1. What is quantum computing?

Quantum computing is a type of computing that uses quantum-mechanical phenomena, such as superposition and entanglement, to perform operations on data. This allows for more efficient and powerful processing of information compared to classical computing.

## 2. How does quantum computing work?

Quantum computing uses quantum bits, or qubits, instead of classical bits to store and process information. These qubits can exist in multiple states at once, allowing for parallel computation and increased processing power. Quantum algorithms are designed to take advantage of this unique property of qubits.

## 3. What are the potential applications of quantum computing?

Quantum computing has the potential to revolutionize many industries, such as finance, healthcare, and cybersecurity. It can be used for tasks such as optimization, simulation, and machine learning, which are difficult or impossible for classical computers to perform efficiently.

## 4. Do I need to know quantum mechanics to understand quantum computing?

While a basic understanding of quantum mechanics can be helpful, it is not necessary to understand the fundamentals of quantum computing. Many resources and tutorials are available for beginners to learn about quantum computing without prior knowledge of quantum mechanics.

## 5. How can I get started with quantum computing?

There are several ways to get started with quantum computing, such as learning programming languages specifically designed for quantum computing, such as Qiskit or Cirq. Additionally, there are online courses and tutorials available for beginners, and some universities offer courses or programs in quantum computing.

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