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MIT researchers have made a significant advance on the road toward the full realization of quantum computation, demonstrating a technique that eliminates common errors in the most essential operation of quantum algorithms, the two-qubit operation or gate.

Despite tremendous progress toward being able to perform computations with low error rates with superconducting quantum bits (qubits), errors in two-qubit gates, one of the building blocks of quantum computation, persist, says Youngkyu Sung, an MIT graduate student in electrical engineering and computer science who is the lead author of a paper on this topic published today in Physical Review X. We have demonstrated a way to sharply reduce those errors.

In quantum computers, the processing of information is an extremely delicate process performed by the fragile qubits, which are highly susceptible to decoherence, the loss of their quantum mechanical behavior. In previous research conducted by Sung and the research group he works with, MIT Engineering Quantum Systems, tunable couplers were proposed, allowing researchers to turn two-qubit interactions on and off to control their operations while preserving the fragile qubits. The tunable coupler idea represented a significant advance and was cited, for example, by Google as being key to their recent demonstration of the advantage that quantum computing holds over classical computing.

Still, addressing error mechanisms is like peeling an onion: Peeling one layer reveals the next. In this case, even when using tunable couplers, the two-qubit gates were still prone to errors that resulted from residual unwanted interactions between the two qubits and between the qubits and the coupler. Such unwanted interactions were generally ignored prior to tunable couplers, as they did not stand out but now they do. And, because such residual errors increase with the number of qubits and gates, they stand in the way of building larger-scale quantum processors. The Physical Review X paper provides a new approach to reduce such errors.

We have now taken the tunable coupler concept further and demonstrated near 99.9 percent fidelity for the two major types of two-qubit gates, known as Controlled-Z gates and iSWAP gates, says William D. Oliver, an associate professor of electrical engineering and computer science, MIT Lincoln Laboratory fellow, director of the Center for Quantum Engineering, and associate director of the Research Laboratory of Electronics, home of the Engineering Quantum Systems group. Higher-fidelity gates increase the number of operations one can perform, and more operations translates to implementing more sophisticated algorithms at larger scales.

To eliminate the error-provoking qubit-qubit interactions, the researchers harnessed higher energy levels of the coupler to cancel out the problematic interactions. In previous work, such energy levels of the coupler were ignored, although they induced non-negligible two-qubit interactions.

Better control and design of the coupler is a key to tailoring the qubit-qubit interaction as we desire. This can be realized by engineering the multilevel dynamics that exist, Sung says.

The next generation of quantum computers will be error-corrected, meaning that additional qubits will be added to improve the robustness of quantum computation.

Qubit errors can be actively addressed by adding redundancy, says Oliver, pointing out, however, that such a process only works if the gates are sufficiently good above a certain fidelity threshold that depends on the error correction protocol. The most lenient thresholds today are around 99 percent. However, in practice, one seeks gate fidelities that are much higher than this threshold to live with reasonable levels of hardware redundancy.

The devices used in the research, made at MITs Lincoln Laboratory, were fundamental to achieving the demonstrated gains in fidelity in the two-qubit operations, Oliver says.

Fabricating high-coherence devices is step one to implementing high-fidelity control, he says.

Sung says high rates of error in two-qubit gates significantly limit the capability of quantum hardware to run quantum applications that are typically hard to solve with classical computers, such as quantum chemistry simulation and solving optimization problems.

Up to this point, only small molecules have been simulated on quantum computers, simulations that can easily be performed on classical computers.

In this sense, our new approach to reduce the two-qubit gate errors is timely in the field of quantum computation and helps address one of the most critical quantum hardware issues today, he says.

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Clearing the way toward robust quantum computing - MIT News

Cryptocurrency

Theres been a lot of focus recently on encryption within the context of cryptocurrencies. Taproot being implemented in bitcoin has led to more cryptographic primitives that make the bitcoin network more secure and private. Its major upgrade from a privacy standpoint is to make it impossible to distinguish between multi-signature and single-signature transactions. This will, for example, make it impossible to tell which transactions involve the opening of Lightning Network channels versus regular base layer transactions. The shift from ECDSA signatures to Schnorr signatures involves changes and upgrades in cryptography.

Yet these cryptographic primitives might need to shift or transition in the face of new computers such as quantum computers. If you go all the way back down to how these technologies work, they are built from unsolved mathematical problems something humans havent found a way to reduce down to our brains capacity for creativity yet limited memory retrieval, or a computers way of programmed memory retrieval. Solving those problems can create dramatic breaks in current technologies.

I sat down with Dr. Jol Alwen, the chief cryptographer of Wickr, the encrypted chat app, to talk about post-quantum encryption and how evolving encryption standards will affect cryptocurrencies. Heres a summary of the insights:

Despite all of the marketing hype around quantum computing and quantum supremacy, the world isnt quite at the stage where the largest (publicly disclosed) quantum computer can meaningfully break current encryption standards. That may happen in the future, but commercially available quantum computers now cannot meaningfully dent the encryption standards cryptocurrencies are built on.

Quantum computer and encryption experts are not communicating with one another as much as they should. This means that discrete advances in quantum computing may happen with a slight lag in how encryption would operate. Its been the case that nation-states, such as China, have been going dark on research related to quantum this has the effect of clouding whether or not serious attempts can be made on the encryption standards of today, and disguising the sudden or eventual erosion of encryption a sudden break that might mean devastation for cryptocurrencies and other industries that rely on cryptography.

Its been known that many encryption schemes that defeat classical computers may not be able to defeat a sufficiently powerful quantum computer. Grovers algorithm is an example. This is a known problem and with the continued development of quantum computers, will likely be a significant problem in a matter of time.

Encryption standards being diluted now is not only a risk for the future, but also an attack on the conversations and transactions people will have to remain private in the past as well. Past forms of encryption that people relied upon would be lost the privacy they assumed in the past would be lost as well.

Cryptographic primitives are baked into cryptocurrencies regardless of their consensus algorithm. A sudden shift in encryption standards will damage the ability for proof-of-work miners or those looking to demonstrate the cryptographic proof that theyve won the right to broadcast transactions in the case of proof-of-stake designs such as the one proposed by Ethereum. Digital signatures are the common point of vulnerability here, as well as the elliptic curve cryptography used to protect private keys.

Everything here breaks if the digital signatures are no longer valid anybody with access to public keys could then spend amounts on other peoples behalf. Wallet ownership would be up for grabs. says Dr. Alwen. Proof-of-work or proof-of-stake as a consensus algorithm would be threatened as well in all cases, the proof would no longer be valid and have it be authenticated with digital signatures anybody could take anybody elses blocks.

While proof-of-work blocks would have some protection due to the increasingly specialized hardware (ASICs) being manufactured specifically for block mining, both systems would have vulnerabilities if their underlying encryption scheme were weakened. Hashing might be less threatened but quantum compute threatens key ownership and the authenticity of the system itself.

Post-quantum encryption is certainly possible, and a shift towards it can and should be proactive. Theres real stuff we can do. Dr. Alwen says here. Bitcoin and other cryptocurrencies may take some time to move on this issue, so any preparatory work should be regarded as important, from looking at benefits and costs you can get a lot of mileage out of careful analysis.

Its helped here by the fact that there is a good bottleneck in a sense: there are only really two or three types of cryptographic techniques that need replacement. Digital signatures and key agreement are the two areas that need the focus. Patching these two areas will help the vast majority of vulnerabilities that might come from quantum computation.

Its important to note that a sudden and critical break in encryption would affect other industries as well and each might have different reasons why an attack would be more productive or they might be more slow to react. Yet if there were a revolution tomorrow, this would pose a clear and direct threat to the decentralization and security promises inherent in cryptocurrencies. Because of how important encryption and signatures are to cryptocurrencies, its probable that cryptocurrency communities will have many more debates before or after a sudden break, but time would be of the essence in this scenario. Yet, since encryption is such a critical part of cryptocurrencies, there is hope that the community will be more agile than traditional industries on this point.

If a gap of a few years is identified before this break happens, a soft fork or hard fork that the community rallies around can mitigate this threat along with new clients. But it requires proactive changes and in-built resistance, as well as keeping a close eye on post-quantum encryption.

It is likely that instead of thinking of how to upgrade the number of keys used or a gradual change, that post-quantum encryption will require dabbling into categories of problems that havent been used in classical encryption. Dr. Alwen has written about lattice-based cryptography as a potential solution. NIST, the National Institute of Standards and Technology currently responsible for encryption standards has also announced a process to test and standardize post-quantum public-key encryption.

Hardware wallets are in principle the way to go now for security in a classical environment Dr. Alwen points out, having done research in the space. The fact that theyre hard to upgrade is a problem, but its much better than complex devices like laptops and cell phones in terms of the security and focus accorded to the private key.

In order to keep up with cryptography and its challenges, MIT and Stanford open courses are a good place to start to get the basic terminology. There is for example, an MIT Cryptography and Cryptanalysis course on MIT OpenCourseWare and similar free Stanford Online courses.

There are two areas of focus: applied cryptography or theory of cryptography. Applied cryptography is a field that is more adjacent to software engineering, rather than math-heavy cryptography theory. An important area is to realize what role suits you best when it comes to learning: making headway on breaking cryptography theory or understanding from an engineering perspective how to implement solid cryptography.

When youre a bit more advanced and focused on cryptography theory, Eprint is a server that allows for an open forum for cryptographers to do pre-prints. Many of the most important developments in the field have been posted there.

Forums around common cryptography tools help with applied cryptography as well as some of the cryptography theory out there: the Signal forums, or the Wickr blog are examples.

Cryptocurrencies are co-evolving with other technologies. As computers develop into different forms, there are grand opportunities, from space-based cryptocurrency exchange to distributed devices that make running nodes accessible to everybody.

Yet, in this era, there will also be new technologies that force cryptocurrencies to adapt to changing realities. Quantum computing and the possibility that it might eventually break the cryptographic primitives cryptocurrencies are built on is one such technology. Yet, its in the new governance principles cryptocurrencies embody that might help them adapt.

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Here's How Quantum Computers Will Really Affect Cryptocurrencies - Forbes

Quantum computing potential extends beyond simply processing things faster, offering scope to create entire new consumer services and product offerings

Neil Cumins Thursday, 17 June, 2021

Its common for new technologies to be treated with a healthy degree of scepticism when theyre first unveiled.

From the internet to social media, it often takes a while for potential to become reality.

Today, theres excitable talk about the blockchains potential, or how light-powered LiFi may supplant WiFi in the nations homes. Talk, but not much action as yet.

Quantum computing potential may be unmatched in terms of transforming our world even more so than the Internet of Things, or fully automated robotics.

And while you dont need a degree in quantum physics to understand quantum computing, its important to appreciate the basics of this highly complex (and unstable) technology.

Regardless of what theyre being asked to do, electronic devices only understand binary inputs. Zero or one, on or off. Thats it.

Every FIFA tournament, CAD package, Netflix marathon and email is composed of immense strings of zeroes and ones the binary data bits computers can process and interpret.

Quantum computing potentially subverts this by allowing bits to be both zeroes and ones at the same time.

This status fluidity involves holding data in whats called a superposition state a coin spinning on its side rather than landing heads-up or tails-up.

Superpositions grant a single bit far more potential, offering exponentially more processing power than a modern (classical) computer can deliver.

Quantum computers are theoretically capable of achieving feats todays hardware couldnt manage in a hundred lifetimes.

Google claims to own a quantum computer which can perform tasks 100,000,000 times faster than its most powerful classical computer.

Indeed, computer scientists have already demonstrated that quantum processing can encrypt data in such a way it becomes impossible to hack.

This alone could transform online security, rendering spyware and most modern malware redundant, while ensuring a far safer world for consumers and businesses.

Quantum computing may be able to process the vast repositories of digital information being generated by billions of AI devices, which would otherwise result in huge data siloes.

It could unlock the secrets of our universe, helping us to achieve nuclear fusion or test drugs in ways wed never be able to accomplish with classical computing and brainpower alone.

Unfortunately, there are certain obstacles in the way of achieving full quantum computing potential.

The molecular instability involved in superpositions requires processors to be stored at cryogenic temperatures as close to absolute zero (-273C) as possible.

Devices need to be stored and handled with exceptional care, which in turn makes them incredibly expensive and unsuitable for domestic deployment.

And while the ability to develop uncrackable encryption algorithms is appealing, a quantum processor could also unlock almost any existing encryption method.

The havoc that could wreak in the wrong hands doesnt bear thinking about, and scientists are struggling to develop quantum-resistant algorithms for classical computers.

Like all emerging technologies, quantum computing has some way to go before it achieves mainstream adoption and acceptance.

When it does, the world will be a very different place.

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Is quantum computing about to change the world? - BroadbandDeals

Intel's 17-qubit quantum test chip.

Source: Intel

Stefan Thomas really could have used a quantum computer this year.

The German-born programmer and crypto trader forgot the password to unlock his digital wallet, which contains 7,002 bitcoin, now worth $265 million. Quantum computers, which will be several million times faster than traditional computers, could have easily helped him crack the code.

Though quantum computing is still very much in its infancy, governments and private-sector companies such as Microsoft and Google are working to make it a reality. Within a decade, quantum computers could be powerful enough to break the cryptographic security that protects cell phones, bank accounts, email addresses and yes bitcoin wallets.

"If you had a quantum computer today, and you were a state sponsor China, for example most probably in about eight years, you could crack wallets on the blockchain," said Fred Thiel, CEO of cryptocurrency mining specialist Marathon Digital Holdings.

This is precisely why cryptographers around the world are racing to build a quantum-resistant encryption protocol.

Right now, much of the world runs on something called asymmetric cryptography, in which individuals use a private and public key pair to access things such as email and crypto wallets.

"Every single financial institution, every login on your phone it is all based on asymmetric cryptography, which is susceptible to hacking with a quantum computer," Thiel said. Thiel is a former director of Utimaco, one of the largest cryptography companies in Europe, which has worked with Microsoft, Google and others on post-quantum encryption.

The public-private key pair lets users produce a digital signature, using their private key, which can be verified by anyone who has the corresponding public key.

In the case of cryptocurrencies such as bitcoin, this digital signature is called the Elliptic Curve Digital Signature Algorithm, and it ensures that bitcoin can only be spent by the rightful owner.

Theoretically, someone using quantum computing could reverse-engineer your private key, forge your digital signature, and subsequently empty your bitcoin wallet.

"If I was dealing in fear-mongering ... I'd tell you that among the first types of digital signatures that will be broken by quantum computers are elliptic curves, as we use them today, for bitcoin wallets," said Thorsten Groetker, former Utimaco CTO and one of the top experts in the field of quantum computing.

"But that would happen if we do nothing," he said.

Crypto experts told CNBC they aren't all that worried about quantum hacking of bitcoin wallets for a couple of different reasons.

Castle Island Ventures founding partner Nic Carter pointed out that quantum breaks would be gradual rather than sudden.

"We would have plenty of forewarning if quantum computing was reaching the stage of maturity and sophistication at which it started to threaten our core cryptographic primitives," he said. "It wouldn't be something that happens overnight."

There is also the fact that the community knows that it is coming, and researchers are already in the process of building quantum-safe cryptography.

"The National Institute of Science and Technology (NIST) has been working on a new standard for encryption for the future that's quantum-proof," said Thiel.

NIST is running that selection process now, picking the best candidates and standardizing them.

"It's a technical problem, and there's a technical solution for it," said Groetker. "There are new and secure algorithms for digital signatures. ... You will have years of time to migrate your funds from one account to another."

Groetker said he expects the first standard quantum-safe crypto algorithm by 2024, which is still, as he put it, well before we'd see a quantum computer capable of breaking bitcoin's cryptography.

Once a newly standardized post-quantum secure cryptography is built, Groetker said, the process of mass migration will begin. "Everyone who owns bitcoin or ethereum will transfer [their] funds from the digital identity that is secured with the old type of key, to a new wallet, or new account, that's secured with a new type of key, which is going to be secure," he said.

However, this kind of upgrade in security requires users to be proactive. In some scenarios, where fiat money accounts are centralized through a bank, this process may be easier than requiring a decentralized network of crypto holders to update their systems individually.

"Not everybody, regardless of how long it takes, will move their funds in time," said Groetker. Inevitably, there will be users who forget their password or perhaps passed away without sharing their key.

"There will be a number of wallets ... that become increasingly insecure, because they're using weaker keys."

But there are ways to deal with this kind of failing in security upgrade. For example, an organization could lock down all accounts still using the old type of cryptography and give owners some way to access it. The trade-off here would be the loss of anonymity when users go to reclaim their balance.

Continued here:
Hacking bitcoin wallets with quantum computers could happen but cryptographers are racing to build a workaround - CNBC

Image credit: Russell Huffman

By Ryan F. Mandelbaum and Olivia Lanes

What is Quantum Computing? Most of this blogs readers are already excited about this technology after all, weve spent many hours reading textbooks and documentation trying to figure out how to write programs for real quantum chips. But many of our friends, family members, and people we randomly encounter still scratch their heads when they hear the words quantum and computer put together. We think its high time that they learn about quantum computing, too.

Partially inspired by Talia Gershons awesome WIRED video where she explains quantum computing at five different difficulty levels, we came up with some stock quantum computing explanations you can use to start spreading your excitement for quantum computing to other people in your life (or, if youre new here, use to understand quantum yourself). While were excited about this technology, we tried our best to sidestep the hype; quantum computers are exciting enough on their own, and theres no need to exaggerate how far along they are, what they can do today, or what we hope theyll do in the future.

But, no matter who youre trying to explain quantum to, theres a core understanding we think everyone should have. A quantum computer is similar to a classical computer in a lot of ways. Just like a classical computer, you store information using some physical system. You have to initialize that system, then perform some sort of operations on it (in other words, run a program), and then extract the information. It differs from classical computing in two key elements, however:

These core counterintuitive ideas underlie the fundamental operations of quantum computing. Once you understand these two pieces, the rest is a matter of how deep youd like to learn, and how quantum algorithms might provide benefits to you, your life, or the industry you work in. You should also get started using Qiskit.

Each of these explanations are based mainly on our experiences and opinions, and you might have your own tricks to help get quantum computing across feel free to tell us about them, what worked, and what didnt in the comments!

Some problems are really hard for todays computers to tackle, like designing drugs, running machine learning algorithms, and solving certain kinds of math equations. But the ability to solve those problems could help humankind tackle some of its biggest challenges. Well, quantum computers represent a new kind of computing system under development today that solves problems using an architecture that follows the most fundamental laws of nature and we hope theyll one day be able to to solve these hard problems. You can even try them out for yourself.

Hey, you know what a computer is but do you know how it works? Well basically, it thinks of everything, the YouTube videos you watch, the letters on the screen, everything, in a special kind of code. Programs and apps are basically just instructions that change the code around, leading to the results you see on the screen. But theres only so many different kinds of things that a regular computer can do with that code. A quantum computer works similarly to a regular computer, but its code looks a little different, and it can do even more things to those codes than your parents computers can. Quantum computers are really new, so theyre not better than a regular computer juuust yet but we think that one day they might be able to solve some of the biggest challenges in the world. Maybe it will even help you do your homework faster or something.

What do I do for work? Well *cracks knuckles*

So, there are some problems that people would like to solve that take even the best supercomputers a ridiculously long amount of time to run problems like simulating chemistry or breaking big numbers into smaller factors. Quantum computers might be able to tackle these problems by relying on a different set of physical laws than your computer does. Your computer is really just lots of electrical switches, called bits, that represents everything using binary code. In other words, the language your computer speaks encodes everything as long strings of 0s or 1s, while programs are mathematical operations that can change zeros to ones and vice versa. However, at even at the most fundamental level, a quantum computers code and its corresponding hardware looks differently. Quantum bits, or qubits, dont have to be binary during the calculation; they can actually exist in well-defined combinations of 0 and 1.

Its kind of like, if I was a qubit, instead of having mashed potatoes OR asparagus, I can have a third of a helping of mashed potatoes and two thirds of a helping of asparagus so long as it adds up to a whole side dish. However, once the problem ends, the quantum computers can only give answers in binary code, with some probability determining the outcome. Its like, if someone wanted to know which side dish I had, they check by closing their eyes, shoving their fork onto my plate, and reporting only the first side dish they taste, with the probabilities determined by how much of each side I had on my plate when they went in for a bite. Qubits also interact differently from regular bits. Lets say that Olivia and Ryan are both at dinner, and you only know that between them theyve eaten a helping of potatoes and a helping of asparagus, and not whose dish has what sides on it. But even if they havent spoken since dinner started, if you did the same eyes-closed fork jab you did on my plate, the sides they picked will be more correlated than the usual rules of random guessing would allow.

A direct consequence of this quantum dinner behavior is that there exist different types of algorithms for quantum computers. In fact, due to the quantum nature of the processor, scientists have already shown that at least theoretically, some quantum algorithms can be run exponentially faster than their classical counterparts. Provided that we can build the hardware, all these sorts of near-impossible problems may one day have solutions within arms reach. Anyway, thats what I do at work. Can you pass the gravy?

Editor Note: While thankfully we havent encountered a large contingency of quantum computing conspiracies, hype and tabloid coverage has led to some worrying interpretations of what quantum can and cant do some indeed bordering on conspiracy-minded thinking. But according to at least one expert, the best way to speak with conspiracy theorists isnt with facts but with empathy.

Oh, youre worried about quantum computers? Whys that? I was actually really interested in learning more about them, too, and I didnt understand them at first. What have you learned so far? Huh, thats interesting. So far, Ive learned that some research labs are working on a new kind of computer that can solve certain problems that classical computers cant. I was definitely really interested in the science behind it. See, theyre more or less just computer processors that rely on a system of bits to solve problems. However, these quantum bits can perform a richer set of mathematical operations than classical bits, which makes them better at solving certain problems. What did you read that they could do? Portals and new dimensions, huh? Thats really interesting, but no, I did some research on my own and what the media doesnt want you to know is that these computers are more business-y than science fiction-y they might one day be revolutionary for chemistry, machine learning, and other topics. But the media also doesnt want you to know that these computers are still really early in their development like, they forget their information quickly and theres a lot of work to do before theyre something to worry about. There are actually services that let you try them out and program them on your own. Now tell me more about the UFO you saw

Quantum computers are a new kind of computer processor that one day might augment your current computing resources to tackle certain challenges difficult for todays classical computers alone. Quantum processors work in tandem with classical computers as part of a cloud-based computing workflow, providing value by performing mathematical operations challenging for classical processors. While theres no device capable of executing a killer app yet, research has demonstrated that the enhanced capabilities of quantum systems could accelerate the research and development process, and provide value to certain industries in the coming years chemical and materials design, drug development, finance, and machine learning, for example. In one report, Boston Consulting Group predicted that productivity gains by end users of quantum computing, both in cost savings and revenue generation opportunities, could equal $450 billion or more annually. Many Fortune-500 companies have already begun to research and develop domain-specific thought leadership in quantum computing so as to be prepared when the field matures.

Quantum processors are kind of like a GPU in the sense that theyre designed to handle specific tasks that the CPU isnt well-suited to handle. But unlike a GPU, quantum computers work using a different kind of hardware architecture, one that allows them to perform a richer array of logical operations than just Boolean logic. These hardware requirements lead to bulky systems, so todays developers hoping to exploit quantum resources run their code over the cloud, employing both classical and quantum processing power where necessary for their program.

Quantum computers are a nascent technology, so programming them today is can be a lot like writing code in assembly language, stringing individual quantum bits together into circuits using quantum logic gates. These circuits are similar to classical computers in that their programs begin by initializing the qubits into a string of zeroes and ones, then perform operations, then return an output. However, quantum gates can also produce superpositions of strings, creating well-defined combinations of bitstrings (though you can only end up with one of these bitstrings, determined by the rules of probability, at the end of the calculation). Further operations produce entanglement and interference, linking certain qubits together and changing those probability distributions such that certain bitstrings become more likely and certain bitstrings become less likely when you measure the final result.

Given how recently quantum programming languages arose, developers have organized into open source communities like Qiskit where they maintain the code used to access quantum computers. As part of that, theyre designing and implementing quantum algorithms that can run on these devices, and creating modules designed to harness the potential power of quantum computers without having to continually program individual bits kind of like building a higher-level programming language on top of the assembly language with which we access quantum computers today. You can learn more by getting started with Qiskit here!

Quantum mechanics might be confusing, but it can still be incredibly useful, even if youre not a physicist. A computer based on the laws of quantum physics might help solve problems in chemistry, machine learning, or even solving partial differential equations.

Objects following the rules of quantum mechanics can enter states called superpostions. If an objects state is in a superposition of 0 and 1, that means that the object is in a linear combination of both values simultaneously until a measurement forces the object into one state or the other, with the probability of measuring either state based on the coefficients of each state in the linear combination. These objects can also become entangled, meaning you cannot describe one object mathematically on its own; when we perform experiments on entangled particles, we find that their properties are more correlated than classical physics would otherwise allow. We use these principles to construct sets of quantum bits, or qubits. I cant know each qubit value individually I can only create these linear combinations from states that include both qubits. But if I measure one qubit and force it to choose, lets say it ends up measuring 1, then the other qubit will take on a value highly correlated with the first value more correlated than random chance alone would allow. We use these ideas to generate interference, where certain combinations of qubit values become more likely and certain ones become less likely.

In a classical computer, computational spaces add together, because bits can exist in only one state or the other, 0 or 1. In a quantum computer, the computational space grows exponentially as you add more bits (2^n where n is the number of bits) so its easy to understand how they can become powerful computational tools. Furthermore, there are certain problems that are hard for classical computers to compute. Because quantum computers themselves rely on quantum physics, they are better able to simulate quantum mechanical phenomena, like chemical interactions and bonds. Though the devices are noisy and error prone today, researchers hope that quantum computers will be able to utilize the properties of entanglement and interference to run some algorithms faster than a classical computer can, making solutions to these hard problems finally feasible. Together, these benefits might one day allow scientists to perform various elements of their jobs faster.

Macroscopic quantum effects have long been observed in superconducting circuits. However, it wasnt until theoretical developments showing that flux and voltage can be quantized circuit QED that this idea was applied to quantum information processing.

A superconducting transmon qubit is essentially a quantized anharmonic oscillator. The circuits macro state can be described by the quantized energy levels; the ground state (0), the excited state (1), or even higher order excited states as well (2, 3, 4, etc.). But because the circuit is anharmonic the energy transitions between states 0 and 1 is different than 1 and 2, so we can isolate the bottom levels with a microwave pulse at that frequency to create a quantum bit for information processing.

In order to read-out and control the state of a transmon, we couple the qubit to either a 2D or 3D resonator (the physics is the same). The qubit and the resonator interact in such a way that when we probe the resonator with a standing microwave tone, the resonant frequency will actually shift depending on if the qubit is in the ground or excited state. This is how we can read out and interact with the qubits that make up a quantum computer.

Coupling these qubit-cavity systems together in an array and allowing them to talk to other another with 2-qubit gates (essentially more finely tuned microwave pulses) creates a quantum processor. Running specific gates in a specific order on this processor can create quantum algorithms. By leveraging the processors quantum properties of entanglement, superposition and interference, some quantum algorithms can theoretically be run significantly faster than their classical counterparts. Once we have reached the point where applying these algorithms has become useful and advantageous, we will have achieved what we call the era of quantum advantage.

Whispers: Hey there, pup, listen. I told my boss I would be able to teach you quantum computing, but you barely understand how your doggy door works. So heres what Im gonna do. Im gonna train you how to give me your left paw when I say initialize. Then youre gonna give me your right paw when I say X-gate. Then when I say Hadamard gate, youre going to hop on your hind legs and give me both paws. When I say CNOT, youre going to roll over, and when I say measure, youre going to bark. If you do this for me Ill cut some salami up into your dinner tonight.

Hey, Boss! Yeah! I finally figured out how to explain quantum computing to the dog! Yep, Ill write it all down in the blog post tonight. Wanna see?

Get started using Qiskit here!

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How Do You Explain Quantum Computing To Your Dog (And Other Important People in Your Life)? - Medium