Quantum computing just plain sounds cool. Weve all read about the massive investment in making it a reality, and its promise of breakthroughs in many industries. But all that press is usually short on what it is and how it works. Thats for a reason: Quantum computing is quite different from traditional digital computing and requires thinking about things in a non-intuitive way. Oh, and there is math. Lots of it.
This article wont make you an expert, but it should help you understand what quantum computing is, why its important, and why its so exciting. If you already have a background in quantum mechanics and grad school math, you probably dont need to read this article. You can jump straight into a book like A Gentle Introduction To Quantum Computing (Hint, gentle is a relative term). But ifyoure like most of us and dont have that background, lets do our best to demystify one of the most mystical topics in computing.
In a few short paragraphs, here are the basics that well go over in more detail in this article: Quantum computers use qubits instead of traditional bits (binary digits). Qubits are different from traditional bits because until they are read out (meaning measured), they can exist in an indeterminate state where we cant tell whether theyll be measured as a 0 or a 1. Thats because of a unique property called superposition.
Superposition makes qubits interesting, but their real superpower is entanglement. Entangled qubits can interact instantly. To make functional qubits, quantum computers have to be cooled to near absolute zero. Even when supercooled, qubits dont maintain their entangled state (coherence) for very long.
That makes programming them extra tricky. Quantum computers are programmed using sequences of logic gates of various kinds, but programs need to run quickly enough that the qubits dont lose coherence before theyre measured. For anyone who took a logic class or digital circuit design using flip-flops, quantum logic gates will seem somewhat familiar, although quantum computers themselves are essentially analog. However, the combination of superposition and entanglement make the process about a hundred times more confusing.
The ordinary bits we use in typical digital computers are either 0 or 1. You can read them whenever you want, and unless there is a flaw in the hardware, they wont change. Qubits arent like that. They have a probability of being 0 and a probability of being 1, but until you measure them, they may be in an indefinite state. That state,along with some other state information that allows for additional computational complexity, can be described as being at an arbitrary point on a sphere (of radius 1), that reflects both the probability of being measured as a 0 or 1 (which are the north and south poles).
The qubits state is a combination of the values along all three axes. This is called superposition. Some texts describe this property as being in all possible states at the same time, while others think thats somewhat misleading and that were better off sticking with the probability explanation. Either way, a quantum computer can actually do math on the qubit while it is in superposition changing the probabilities in various ways through logic gates before eventually reading out a result by measuring it. In all cases, though, once a qubit is read, it is either 1 or 0 and loses its other state information.
Qubits typically start life at 0, although they are often then moved into an indeterminate state using a Hadamard Gate, which results in a qubit that will read out as 0 half the time and 1 the other half. Other gates are available to flip the state of a qubit by varying amounts and directions both relative to the 0 and 1 axes, and also a third axis thatrepresents phase, and provides additional possibilities for representing information. The specific operations and gates available depend on the quantum computer and toolkit youre using.
Groups of independent qubits, by themselves, arent enough to create the massive breakthroughs that are promised by quantum computing. The magic really starts to happen when the quantum physics concept of entanglement is implemented. One industry expert likened qubits without entanglement as being a very expensive classical computer. Entangled qubits affect each other instantly when measured, no matter far apart they are, based on what Einstein euphemistically called spooky action at a distance. In terms of classic computing, this is a bit like having a logic gate connecting every bit in memory to every other bit.
You can start to see how powerful that might be compared with a traditional computer needing to read and write from each element of memory separately before operating on it. As a result, there are multiple large potential gains from entanglement. The first is a huge increase in the complexity of programming that can be executed, at least for certain types of problems. One thats creating a lot of excitement is the modeling of complex molecules and materials that are very difficult to simulate with classical computers. Another might be innovations in long-distance secure communications if and when it becomes possible to preserve quantum state over large distances. Programming using entanglement typically starts with the C-NOT gate, which flips the state of an entangled particle if its partner is read out as a 1. This is sort of like a traditional XOR gate, except that it only operates when a measurement is made.
Superposition and entanglement are impressive physical phenomena, but leveraging them to do computation requires a very different mindset and programming model. You cant simply throw your C code on a quantum computer and expect it to run, and certainly not to run faster. Fortunately, mathematicians and physicists are way ahead of the computer builders here, having developed clever algorithms that take advantage of quantum computers decades before the machines started to appear.
Some of the first quantum algorithms created, and honestly, some of the few useful ones Ive found that you can understand without a graduate degree in math, are for secure cryptographic key distribution. These algorithms use the property of entanglement to allow the key creator to send one of each of many pairs of qubits to the recipient. The full explanation is pretty long, but the algorithms rely on the fact that if anyone intercepts and reads one of the entangled bits en route, the companion qubit at the sender will be affected. By passing some statistics back and forth, the sender and receiver can figure out whether the key was transmitted securely, or was hacked on the way.
You may have read that quantum computers one day could break most current cryptography systems. They will be able to do that because there are some very clever algorithms designed to run on quantum computers that can solve a hard math problem, which in turn can be used to factor very large numbers. One of the most famous is Shors Factoring Algorithm. The difficulty of factoring large numbers is essential to the security of all public-private key systems which are the most commonly used today. Current quantum computers dont have nearly enough qubits to attempt the task, but various experts predict they will within the next 3-8 years. That leads to some potentially dangerous situations, such as if only governments and the super-rich had access to the ultra-secure encryption provided by quantum computers.
There are plenty of reasons quantum computers are taking a long time to develop. For starters, you need to find a way to isolate and control a physical object that implements a qubit. That also requires cooling it down to essentially zero (as in .015 degrees Kelvin, in the case of IBMs Quantum One). Even at such a low temperature, qubits are only stable (retaining coherence) for a very short time. That greatly limits the flexibility of programmers in how many operations they can perform before needing to read out a result.
Not only do programs need to be constrained, but they need to be run many times, as current qubit implementations have a high error rate. Additionally, entanglement isnt easy to implement in hardware either. In many designs, only some of the qubits are entangled, so the compiler needs to be smart enough to swap bits around as needed to help simulate a system where all the bits can potentially be entangled.
The good news is that trivial quantum computing programs are actually pretty easy to understand if a bit confusing at first. Plenty of tutorials are available that will help you write your first quantum program, as well as let you run it on a simulator, and possibly even on a real quantum computer.
One of the best places to start is with IBMs QISKit, a free quantum toolkit from IBM Q Research that includes a visual composer, a simulator, and access to an actual IBM quantum computer after you have your code running on the simulator. Rigetti Quantum Computing has also posted an easy intro application, which relies on their toolkit and can be run on their machines in the cloud.
Unfortunately, the trivial applications are just that: trivial. So simply following along with the code in each example doesnt really help you master the intricacies of more sophisticated quantum algorithms. Thats a much harder task.
Thanks to William Poole and Sue Gemmell for their thoughtful input.
Now Read:
Also, check out ourExtremeTech Explainsseries for more in-depth coverage of todays hottest tech topics.
Top image credit: IBM
View post:
How Does Quantum Computing Work? - ExtremeTech
- Mathematician breaks down how to defend against quantum ... - Phys.Org [Last Updated On: February 28th, 2017] [Originally Added On: February 28th, 2017]
- Here Is Everything You Need to Know About Quantum Computers - Interesting Engineering [Last Updated On: March 18th, 2017] [Originally Added On: March 18th, 2017]
- Quantum Computing Market Forecast 2017-2022 | Market ... [Last Updated On: March 18th, 2017] [Originally Added On: March 18th, 2017]
- What is Quantum Computing? Webopedia Definition [Last Updated On: March 18th, 2017] [Originally Added On: March 18th, 2017]
- Quantum computing is about to disrupt the government contracts market - Bloomberg Government (blog) [Last Updated On: April 22nd, 2017] [Originally Added On: April 22nd, 2017]
- Scientists: We Have Detected the Existence of a Fundamentally New State of Matter - Futurism [Last Updated On: April 22nd, 2017] [Originally Added On: April 22nd, 2017]
- What Sorts Of Problems Are Quantum Computers Good For? - Forbes [Last Updated On: April 22nd, 2017] [Originally Added On: April 22nd, 2017]
- quantum computing - WIRED UK [Last Updated On: April 22nd, 2017] [Originally Added On: April 22nd, 2017]
- Inside Microsoft's 'soup to nuts' quantum computing ramp-up - Computerworld Australia [Last Updated On: April 29th, 2017] [Originally Added On: April 29th, 2017]
- Molecular magnets closer to application in quantum computing - Next Big Future [Last Updated On: May 15th, 2017] [Originally Added On: May 15th, 2017]
- The Bizarre Quantum Test That Could Keep Your Data Secure - WIRED [Last Updated On: May 18th, 2017] [Originally Added On: May 18th, 2017]
- IBM boosts power of quantum computing processors as it lays ... - www.computing.co.uk [Last Updated On: May 22nd, 2017] [Originally Added On: May 22nd, 2017]
- IBM makes leap in quantum computing power - ITworld [Last Updated On: May 22nd, 2017] [Originally Added On: May 22nd, 2017]
- Toward mass-producible quantum computers | MIT News - MIT News [Last Updated On: June 2nd, 2017] [Originally Added On: June 2nd, 2017]
- Purdue, Microsoft Partner On Quantum Computing Research | WBAA - WBAA [Last Updated On: June 2nd, 2017] [Originally Added On: June 2nd, 2017]
- Tektronix AWG Pulls Test into Era of Quantum Computing - Electronic Design [Last Updated On: June 2nd, 2017] [Originally Added On: June 2nd, 2017]
- Google to Achieve "Supremacy" in Quantum Computing by the End of 2017 - Big Think [Last Updated On: July 1st, 2017] [Originally Added On: July 1st, 2017]
- Quantum Computing Becomes More Accessible - Scientific American [Last Updated On: July 1st, 2017] [Originally Added On: July 1st, 2017]
- Qudits: The Real Future of Quantum Computing? - IEEE Spectrum - IEEE Spectrum [Last Updated On: July 1st, 2017] [Originally Added On: July 1st, 2017]
- Alkermes and IBM's quantum computing. Who'll be the big winner? Malcolm Berko - Durham Herald Sun [Last Updated On: July 6th, 2017] [Originally Added On: July 6th, 2017]
- Quantum Computers Made Even More Powerful with New microchip generating 'Qudits' - TrendinTech [Last Updated On: July 8th, 2017] [Originally Added On: July 8th, 2017]
- Quantum Computing Record Broken - Wall Street Pit [Last Updated On: July 8th, 2017] [Originally Added On: July 8th, 2017]
- Technique for measuring and controlling electron state is a ... - UCLA Newsroom [Last Updated On: July 9th, 2017] [Originally Added On: July 9th, 2017]
- Quantum cheques could be a forgery-free way to move money - New Scientist [Last Updated On: July 10th, 2017] [Originally Added On: July 10th, 2017]
- Quantum-computer node uses two different ion species - physicsworld.com [Last Updated On: July 10th, 2017] [Originally Added On: July 10th, 2017]
- Quantum Computers vs Bitcoin How Worried Should We Be? - The Merkle [Last Updated On: July 10th, 2017] [Originally Added On: July 10th, 2017]
- Why you might trust a quantum computer with secretseven over ... - Phys.Org [Last Updated On: July 12th, 2017] [Originally Added On: July 12th, 2017]
- Physicists Take Big Step Towards Quantum Computing and ... - Universe Today [Last Updated On: August 1st, 2017] [Originally Added On: August 1st, 2017]
- Quantum Computing Market Worth 495.3 Million USD by 2023 | 08 ... - Markets Insider [Last Updated On: August 10th, 2017] [Originally Added On: August 10th, 2017]
- China uses a quantum satellite to transmit potentially unhackable data - CNBC [Last Updated On: August 10th, 2017] [Originally Added On: August 10th, 2017]
- Blind quantum computing for everyone - Phys.org - Phys.Org [Last Updated On: August 12th, 2017] [Originally Added On: August 12th, 2017]
- Quantum Computing Is Real, and D-Wave Just Open ... - WIRED [Last Updated On: August 12th, 2017] [Originally Added On: August 12th, 2017]
- Machine learning tackles quantum error correction - Phys.Org [Last Updated On: August 15th, 2017] [Originally Added On: August 15th, 2017]
- Quantum Internet Is 13 Years Away. Wait, What's Quantum Internet? - WIRED [Last Updated On: August 15th, 2017] [Originally Added On: August 15th, 2017]
- Physicists Have Made Exotic Quantum States From Light - Futurism [Last Updated On: August 16th, 2017] [Originally Added On: August 16th, 2017]
- $495.3 Million Quantum Computing Market 2017 by Revenue Source, Application, Industry, and Geography - Global ... - PR Newswire (press release) [Last Updated On: August 18th, 2017] [Originally Added On: August 18th, 2017]
- How quantum mechanics can change computing - The Conversation US [Last Updated On: August 23rd, 2017] [Originally Added On: August 23rd, 2017]
- Introducing Australia's first quantum computing hardware company - Computerworld Australia [Last Updated On: August 23rd, 2017] [Originally Added On: August 23rd, 2017]
- IEEE Approves Standards Project for Quantum Computing ... - insideHPC [Last Updated On: August 23rd, 2017] [Originally Added On: August 23rd, 2017]
- Commonwealth Bank investing in Australia's first quantum computer company - Which-50 (blog) [Last Updated On: August 25th, 2017] [Originally Added On: August 25th, 2017]
- How quantum mechanics can change computing - San Francisco ... - San Francisco Chronicle [Last Updated On: August 25th, 2017] [Originally Added On: August 25th, 2017]
- Quantum Computing Is Coming at Us Fast, So Here's Everything You Need to Know - ScienceAlert [Last Updated On: August 27th, 2017] [Originally Added On: August 27th, 2017]
- Quantum computing event explores the implications for business - Cambridge Network [Last Updated On: August 30th, 2017] [Originally Added On: August 30th, 2017]
- Microsoft's Aussie quantum computing lab set to scale up next-gen ... - ARNnet [Last Updated On: September 7th, 2017] [Originally Added On: September 7th, 2017]
- An Entirely New Type of Quantum Computing Has Just Been Invented - Futurism [Last Updated On: September 7th, 2017] [Originally Added On: September 7th, 2017]
- Microsoft just upped its multi-million bet on quantum computing - ZDNet [Last Updated On: September 7th, 2017] [Originally Added On: September 7th, 2017]
- Here's what quantum computing is and why it matters [Last Updated On: October 6th, 2017] [Originally Added On: October 6th, 2017]
- What will you actually use quantum computing for? | ZDNet [Last Updated On: October 11th, 2017] [Originally Added On: October 11th, 2017]
- Quantum Computing | Intel Newsroom [Last Updated On: October 13th, 2017] [Originally Added On: October 13th, 2017]
- Intel Takes First Steps To Universal Quantum Computing [Last Updated On: October 13th, 2017] [Originally Added On: October 13th, 2017]
- Qudits: The Real Future of Quantum Computing? - IEEE Spectrum [Last Updated On: October 13th, 2017] [Originally Added On: October 13th, 2017]
- quantum computing - engadget.com [Last Updated On: October 13th, 2017] [Originally Added On: October 13th, 2017]
- Quantum computing - news.microsoft.com [Last Updated On: November 1st, 2017] [Originally Added On: November 1st, 2017]
- IBM's processor pushes quantum computing ... - engadget.com [Last Updated On: November 16th, 2017] [Originally Added On: November 16th, 2017]
- Yale Professors Race Google and IBM to the First Quantum ... [Last Updated On: November 16th, 2017] [Originally Added On: November 16th, 2017]
- Quantum Computing Is the Next Big Security Risk | WIRED [Last Updated On: December 8th, 2017] [Originally Added On: December 8th, 2017]
- Microsoft offers developers a preview of its quantum ... [Last Updated On: December 12th, 2017] [Originally Added On: December 12th, 2017]
- New silicon structure opens the gate to quantum computers [Last Updated On: December 14th, 2017] [Originally Added On: December 14th, 2017]
- Quantum Computing Explained | What is Quantum Computing? [Last Updated On: December 21st, 2017] [Originally Added On: December 21st, 2017]
- What is Quantum Computing? | SAP News Center [Last Updated On: December 23rd, 2017] [Originally Added On: December 23rd, 2017]
- Is Quantum Computing an Existential Threat to Blockchain ... [Last Updated On: December 25th, 2017] [Originally Added On: December 25th, 2017]
- IBM puts its quantum computer to work in relaxing, nerdy ASMR ... [Last Updated On: January 8th, 2018] [Originally Added On: January 8th, 2018]
- Quantum computing is going to change the world. Here's what ... [Last Updated On: January 8th, 2018] [Originally Added On: January 8th, 2018]
- The Era of Quantum Computing Is Here. Outlook: Cloudy ... [Last Updated On: January 26th, 2018] [Originally Added On: January 26th, 2018]
- What is quantum computing? - Definition from WhatIs.com [Last Updated On: February 5th, 2018] [Originally Added On: February 5th, 2018]
- Senate bills would make quantum computing a priority [Last Updated On: June 10th, 2018] [Originally Added On: June 10th, 2018]
- Two Quantum Computing Bills Are Coming To Congress [Last Updated On: July 5th, 2018] [Originally Added On: July 5th, 2018]
- Quantum Computing Market Research Report- Forecast 2022 | MRFR [Last Updated On: August 1st, 2018] [Originally Added On: August 1st, 2018]
- What Is Quantum Computing? The Complete WIRED Guide | WIRED [Last Updated On: August 22nd, 2018] [Originally Added On: August 22nd, 2018]
- Quantum Computing | USRA [Last Updated On: August 30th, 2018] [Originally Added On: August 30th, 2018]
- The quantum computing race the US cant afford to lose [Last Updated On: September 3rd, 2018] [Originally Added On: September 3rd, 2018]
- The reality of quantum computing could be just three years ... [Last Updated On: September 12th, 2018] [Originally Added On: September 12th, 2018]
- US takes first step toward a quantum computing workforce ... [Last Updated On: September 17th, 2018] [Originally Added On: September 17th, 2018]
- China bet big on quantum computing. Now the ... - money.cnn.com [Last Updated On: September 17th, 2018] [Originally Added On: September 17th, 2018]
- China bet big on quantum computing. Now the US races to ... [Last Updated On: October 26th, 2018] [Originally Added On: October 26th, 2018]
- A new type of quantum computer has smashed every record ... [Last Updated On: December 21st, 2018] [Originally Added On: December 21st, 2018]
- IBM unveils its first commercial quantum computer [Last Updated On: January 9th, 2019] [Originally Added On: January 9th, 2019]
- IBM thinks outside of the lab, puts quantum computer in a box [Last Updated On: January 11th, 2019] [Originally Added On: January 11th, 2019]
- Quantum Computing | The MIT Press [Last Updated On: January 11th, 2019] [Originally Added On: January 11th, 2019]
- CES 2019: IBM's Q System One Is the Rock Star Quantum ... [Last Updated On: January 13th, 2019] [Originally Added On: January 13th, 2019]