The Future is Quantum
How quantum computing is shaping our future
Modern computers, even supercomputers, are based on the principle of classical physics, and this means that they’re limited by a various number of factors, in particular physical ones. In 1959, Richard Feynman challenged the scientific community to employ quantum mechanical principles and properties in the design of new information processing systems.
After years of research, we’re finally seeing some results in the field of Quantum Computing. The premises is that Quantum Machines promises to outstrip even the most capable of today’s — and tomorrow’s — computers and supercomputers.
But let’s start with the basics first.
The magic of Qubits
Whilst “traditional” computers use bits, Quantum computers use Qubits. Physically speaking, these Quantum-bits are typically subatomic particles such as photons or electrons. Because of their nature, generating and managing qubits isn’t easy. Some companies are developing superconducting circuits (that need to be cooled to extremely low temperatures), others trap individual atoms in electromagnetic fields. In both cases, the main goal is to maintain this qubits in a controlled quantum state. Qubits have some quirky quantum properties such as superposition and entanglement.
Not just ones and zeros, but a Superposition
One of the most unique features of qubits is their ability to be in multiple positions in the same instant. This means that a qubits can represent a combination of 1 and 0 at the same time. Researchers manipulates qubits using precision lasers or microwave beams. This allows a quantum computer with several qubits to crunch through a vast number of potential outcomes simultaneously. The final result of a particular calculation emerges only when the qubits are measured, which immediately causes their quantum state to collapse.
“Spooky action at a distance”, also called Entanglement
Even Einstein had some difficulties trying to come up with an explanation for this incredible property of qubits. Entanglement means that two members of a pair (of qubits) exist in a single quantum state. Changing the state of one of the qubits will instantaneously change the state of the other in a predictable way. This happens regardless of the distance by which they’re separated.
Everything sounds amazing, but there’s a problem, Decoherence
By design, qubits are extremely fragile. The slightest change in temperature can cause them to tumble out of superposition. This kind of “disturbance” is known as noise. This noise is the main cause of calculation errors in quantum computers. Researchers are developing algorithms that can compensate for some of these errors, and adding qubits can also improve accuracy. To create a so called “logical” qubit (a highly reliable one) we still need thousands of standard qubits.
Now that we’ve covered the basics, the question is: What are the future applications of quantum computers?
There are a few applications for quantum computers. One of the most promising is using these computers to simulate the behavior of matter (for example in EVs battery chemical compositions or pharmaceutical applications).
The ability of quantum computers to crunch through vast numbers of potential solutions makes them extremely useful in lots of fields. This could potentially help in the development of artificial intelligence.
Another field where quantum is starting to make an impact (for better or for worse) is the secure communication.
Quantum communication as a foundation for a Quantum Internet
Today’s data is usually encrypted and then sent across a network of computers. This information is sent as a stream of bits, electrical or optical pulses representing ones and zeros. This method leaves room for hackers to intercept the data in transit and analyse it without leaving a trace.
Quantum communication uses quantum physics properties seen before to protect data, by sending these particles in a state of superposition (in a state that represents a combination of 1 and 0). The advantage of using qubits for a secure communication is that, if a hacker tries to observe them in transit, their super-fragile state collapses to either a one or a zero.
Some companies have developed ultra-secure network for transmitting highly sensitive data using a process called Quantum Key Distribution (QKD for short).
Quantum Key Distribution
QKD has a mixed approach to data transmission. It involves sending encrypted data as classical bits over networks, while the keys to decrypt the information are encoded and transmitted in a quantum state. In the following illustration we can see how the process works. Shortly, the algorithm uses two methods to verify the validity of the exchange, key sifting (the comparison of a fraction of the sent qubits) and key distillation (used to account for errors caused by decoherence and/or by an hacker that tried to intercept the key).
There are already some QKD networks emerging. The longest one is located in China, and it covers the distance between Beijing and Shanghai. This kind of networks are used primarily by banks and other financial companies to transmit data (usually to and from a datacenter).
Quantum Repeaters
Just like any other type of data transmission that uses materials like fiber-optic cables, these “quantum networks” have long distance problems. Also like classical network, QKD networks use “trusted nodes” as repeaters. Ideally these nodes would be quantum repeaters with quantum processors in them, but we’re not quite there yet. The security risk of these network is big enough that researchers are working on an alternative approach known as Quantum Teleportation.
Quantum Teleportation
This approach relies on one of the quantum properties seen above, entanglement. The basic idea is to create a pair of entangled photons and send one of each pair to the sender and receiver. Once he has one of these entangled photons, in order to “send” the data, the sender lets a memory qubit interact with the photon. When this interaction takes place, the state of the entangled photon changes, changing the state of the receiver’s photon. Once the state has been changed, the sender measures the state of the qubit and send the information to the receiver using a traditional network. Having received these data, the receiver can now work out how his photon has changed and the data that has been teleported. This method could lay the foundation to create a Quantum Internet.
Now that we know what quantum computers are capable of, one can’t help but wonder how this would affect the current cryptography algorithms.
Super powerful quantum computers vs. Cryptography
Almost every service that we use daily uses some sort of encryption algorithm to communicate securely our data. There are two main types of encryption, symmetric and asymmetric, which essentially use so-called trapdoor functions. These functions are relatively easy to compute one way and really hard to reverse-engineer, a task best suited for a quantum computer and its incredible amount of computational power. In 1994 Peter Shor, a researcher at Bell Labs (and now a professor at MIT), developed an algorithm that helps quantum computers to find the prime factors of integers incredibly fast. Shor’s algorithm poses a risk to public key encryption algorithms, which mostly rely on the multiplication of large prime numbers.
It goes without saying that Quantum Computers represents a serious threat to this algorithms, so, how can we prevent these security breaches to occur?
Enter Post-Quantum Cryptography
Post-Quantum Cryptography is the development of new cryptographic approaches that can be implemented with today’s computers that will be “quantum-proof”. One way to achieve such goal is to increase the size of digital keys in order to significantly increase the number of permutations. Another approach involves the use of more complex trapdoor functions, like supersingular isogeny key exchange.
The rapid evolution of quantum computers is putting a lot of pressure on governments and security experts to find one or more solutions to this problem, mainly because encryption technologies are deeply embedded in a wide variety of systems.
What about the future? What is Quantum Supremacy?
Let’s start with the definition of what Quantum Supremacy is:
“It’s the point at which a quantum computer can complete a mathematical calculation that is demonstrably beyond the reach of even the most powerful supercomputer.”
In October 2019, Google reported that they finally achieved Quantum Supremacy, using a processor with programmable superconducting qubits to create quantum states on 53 qubits, occupying a state space 2⁵³ ~ 10¹⁶. This new system took 200 seconds to complete a task that would’ve taken a state-of-the-art supercomputer approximately 10000 years.
By reaching this milestone, they’ve demonstrated that not only quantum speedup is achievable in a real-world system, but also that there are no hidden physical laws.
We’re now entering the era of NISQ (Noisy Intermediate-Scale Quantum) technologies, an era where we can see that quantum computers are, in fact, capable of completing tasks infeasible for classical ones. Having said that, we must realise that these computers won’t be big enough to provide fault-tolerant implementations of the algorithms we know about. The word noisy in the acronym derives from the fact that we don’t have enough qubits to spare for error correction, meaning that we are still directly using the physical layer’s qubits (This means that we’re still years away from implementing some algorithms, like Shor’s algorithm for factoring).
In conclusion
We are seeing a lot of proof-of-concept in the Quantum computing field, and there are a lot of incredible applications, but we still need to figure out some quirks and most important, how to create machines with enough qubits to actually achieve these applications.
