Quantum Blockchains

Recent quantum computing breakthroughs:

• Scientists in China achieve quantum entanglement record with 18 qubits
• Melbourne university team claim 60 qubit quantum computing simulation world record
• Graphene and the atomic crystals that could see next big breakthrough in tech
• Synthetic Diamonds Lead Princeton Team to Quantum Computing Breakthrough

Quantum computers are incredibly powerful machines that take a new approach to processing information

Quantum computers are incredibly powerful machines that take a new approach to processing information. Built on the principles of quantum mechanics, they exploit complex and fascinating laws of nature that are always there, but usually remain hidden from view. By harnessing such natural behavior, quantum computing can run new types of algorithms to process information more holistically. They may one day lead to revolutionary breakthroughs in materials and drug discovery, the optimization of complex manmade systems, and artificial intelligence. We expect them to open doors that we once thought would remain locked indefinitely. Acquaint yourself with the strange and exciting world of quantum computing.

Quantum computers will mark the end of post-silicon era. Qubits will change work and life.

• Create life-saving medicines and solve some of science’s most complex problems
• Real conversation with AI
• Help create more energy-efficient materials, better weather forecasting, and better financial modeling
• Significant threat to cyber-security
• Threaten online banking transactions, all our communications, driverless cars and even our elections
• No human securities trading at all, anymore

Quantum computers cannot break quantum cryptographic codes

A blockchain is a mathematical structure that stores data securely over time. The idea has risen to fame on the back of the Bitcoin boom. Bitcoin relies on blockchains to securely store its related currency transactions.

The security of a blockchain is guaranteed by standard cryptographic functions. These are relatively secure because breaking them requires huge computing resources, which are not generally available. That looks set to change with the emergence of powerful quantum computers. It will be child’s play for such devices to break this kind cryptographic protection. But quantum computers cannot break quantum cryptographic codes, so various groups have suggested adding quantum cryptography to blockchains to guarantee their security.

Quantum cryptography merely adds a quantum layer to the standard blockchain protocol. Instead, Del Rajan and Matt Visser, at the Victoria University of Wellington, in New Zealand, suggest making the entire blockchain a quantum phenomenon.

Their idea is to create a blockchain using quantum particles that are entangled in time. That would allow a single quantum particle to encode the history of all its predecessors in a way that cannot be hacked without destroying it. Such a protocol relies on the laws of physics to guarantee security. However, it also leads to somebody unusual side effects. “This decentralized quantum blockchain can be viewed as a quantum networked time machine,” say Rajan and Visser.

Quantum computing is solving real problems

Within the research sector, scientists have taken the first steps towards using quantum devices to solve problems in chemistry, materials science, nuclear physics and particle physics. In most cases, these problems have been studied by collaborations between scientists and the developers, owners and/or operators of the devices. However, a combination of publicly available software (such as PyQuil, QISKit and XACC) to program quantum computing processors, coupled with improved access to the devices themselves, is beginning to open the field to a much broader array of interested parties. The companies IBM and Rigetti, for instance, allow users access to their quantum computers via the IBM Q Experience and the Rigetti Forest API, respectively. These are cloud-based services: users can test and develop their programs on simulators, and run them on the quantum devices, without ever having to leave their offices.

Quantum blockchains could act like time machines

A newly proposed "quantum blockchain" could lead to blockchain systems impervious to quantum-computer hacking, a new study finds.

This new quantum blockchain can be interpreted as influencing its own past, making it behave like a time machine, the researchers add.

Another example of blockchain is a kind of database that holds records about the past, such as a history of financial or other transactions, that every node in the network can agree on and that does not require a centralized institution to maintain its ongoing accuracy. The most well-known application of blockchains is Bitcoin, but a diverse array of startup companies, corporate alliances, and research projects have explored other potential uses for the technology.

Blockchains might face trouble from another up-and-coming technology: quantum computers. Whereas classical computers switch transistors either on or off to symbolize data as ones and zeroes, quantum computers use quantum bits or qubits that, because of the surreal nature of quantum physics, can be in a state of superposition where they are both 1 and 0 simultaneously.

Superposition lets one qubit perform two calculations at once, and if two qubits are linked through a quantum effect known as entanglement, they can help perform 2^2 or four calculations simultaneously; three qubits, 2^3 or eight calculations; and so on. In principle, a quantum computer with 300 qubits could perform more calculations in an instant than there are atoms in the visible universe. A powerful enough quantum computer could successfully break conventional cryptography, including that protecting blockchains.

Conventional blockchains collect records into blocks of data

Conventional blockchains collect records into blocks of data, which cryptography links in chronological order. If a hacker attempts to tamper with a particular block, the cryptography is designed to invalidate all future blocks following the tampered block.

In the quantum blockchain, the records in a block are encoded into a series of photons that are entangled with each other. These blocks are linked in chronological order through entanglement in time.

As the blocks making up a quantum blockchain are transferred within a network of quantum computers, photons encoding each block get created and then absorbed by the nodes making up the network. However, entanglement links these photons across time, even photons that never existed at the same time.

"Records about past transactions are encoded onto a quantum state that is spread across time," Rajan says.

In this scenario, a hacker cannot tamper with any photon encoding records of the past, since those photons no longer exist in the current time—they already got absorbed. At best, a hacker can attempt to tamper with the most recent photon, the most current block, and successfully doing so would invalidate that block, informing others it got hacked. "This is more desirable than the standard case where an attacker has the ability, in principle, to tamper with any block," Rajan says.

The researchers say that with entanglement in time, measuring the last photon in a block influences the first photon of that block in the past before it got measured. Essentially, current records in a quantum blockchain are not merely linked to a record of the past but rather a record in the past, one that does not exist anymore.

Storing quantum bits of information, or qubits, is really hard

Storing quantum bits of information, or qubits, is a lot harder than storing ordinary binary digits. It’s not simply ones or zeroes, but the whole range of subtle quantum superpositions between them. Electrons can easily slide out of those states if they’re not stored in the right materials, which is why electrical engineers at Princeton are working with a UK manufacturer to create a better storage material — synthetic diamonds — from scratch. They published an account of their success on Thursday in Science.

For decades, physicists, materials engineers, and others have been trying to achieve the conceptual promise of quantum-encrypted communications because the data transferred in that process is theoretically immune to covert surveillance. Any attempt to observe that data between parties — à la the Heisenberg Uncertainty Principle — would fundamentally alter that information, quickly revealing that it was compromised. The problem has been storing and preserving qubits and then converting them to fiber optic-ready photons, and using diamonds appears to be the route toward achieving both. But not just any diamond will do, which is why Princeton’s team has been hard at work creating a synthetic one, as they describe in their paper.

“The properties that we’re targeting are what’s relevant for quantum networks,” electrical engineer Nathalie de Leon tells Inverse. At Princeton, where de Leon is an assistant professor, her team’s focus is essentially inventing quantum hardware. “It’s applications where you want something that has a long storage time, and then also has a good interface with photons so that you can send light over very long distances.”

Photonic interactions

Photonic interactions matter a lot for high-speed international communications because all of the information traveling along fiber optic cables moves through our global infrastructure as discrete photons — cruising at 69 percent of the speed of light. (Nice.)

“That puts a lot of constraints on the optical characteristics,” de Leon says. “As one example, it’s really important that the color be stable. If the color of the photon is jumping around over time, then that’s really bad for these protocols.”

Right now, de Leon’s group is trying to craft a version of these synthetic diamonds that can convert to the standard 1,550-nanometer wavelength on which photons now traverse fiber optic cables. Currently, her team’s synthetic diamonds support 946-nanometer photon wavelengths. (Photon “color” is a bit of a euphemism here since both of these wavelengths are shades of infrared outside the visible spectrum.)