# Quantum…what?

In this post we want to answer and give a notion of what quantum technology is. We will discuss its most revealing aspects, the importance of it and the barriers it will have to overcome for it to be useful. We will deal with four aspects that from out point of view are the most interesting: quantum computation, metrology and quantum internet.

Quantum computation

Quantum computers can speed up certain types of calculations in unimaginable. Problems that use so be solved in exponential time can now be solved in polynomial time and all thanks to the qubit. Qubits differ from classical bits in that they can take any value between 0 and 1, that means, we can express a qubit as $\alpha|0\rangle + \beta |1\rangle$. This leads to being able to create physical states such as entanglement where the quantum state of different qubits cannot be described independently of the state of the others, including when the qubits are separated by a large distance being this the basis of most quantum algorithms.

We use quantum computers for  tasks like, optimization problems, database searching, machine learning any many more. We also normally use them combined with classical computers in order to achieve their best performance.

So what’s the problem with quantum computers? Estimations say that we would need (depending on the quality of the qubits and the problem that we are solving) over a million qubits for quantum computers to be more efficient than actual classical computers. The theory behind them it’s clear and it works, the problem is the hardware and the difficulties that arise when wanting the qubits to be in states like entanglement. Think that IBM’s biggest quantum computer is a bit over 50 qubits although the number of qubits scales up rapidly over the years.

If I had to give my opinion on this, I would say that quantum technology is something worth spending time and research resources on. Just like nuclear fusion is something that can give us great benefits in the long term, even changing the course of humanity.

Metrology

Quantum metrology is nothing else than a way of making more precise measurements by using quantum effects such as quantum entanglement and quantum squeezing being able to encode a lot of information within a few particles. What we want to achieve in quantum metrology is to give precise measurements that haven’t been consider in classical theories. For example, using a classical method like Centra Limit theorem may reduce errors by utilizing an amount that is proportional to n-1/2 but with quantum effects, we can make central limit theorem much more easier limiting the error for an amount proportional to 1/n.

In contrast to quantum computing, quantum metrology doesn’t require large number of qubits in order to be efficient and although it may seem counter-intuitive quantum uncertainty doesn’t make measurements to be less precise.

Quantum internet

Quantum internet will be a network that will allow quantum devices to exchange information through qubits within an environment that takes advantage of the laws of quantum mechanics such as, again, quantum entanglement and superposition.

As we say, quantum Internet can bring interesting improvements to the current Internet. One of the most important would be to achieve a much lower ping, practically non-existent. This would significantly improve communications, something that may not be so noticeable for the home user, but would be for industry in certain sectors.

With quantum internet we will be able to shorten distances, interconnecting equipment which is kilometers appart.

It will also provide security; this is based on the fact that a measurement in quantum mechanics changes the state of the electron. So if you encode a message with quantum particles and you message has been intercepted by a hacker, the hackers measurement will change the behaviour of the particle.

Encryption systems used currently like RSA will be obsolete as they will be easily breakable with quantum computers (in the case of RSA using the algorithm of Shor). That said, there currently exists encryption systems that are already quantum proof).

Quantum simulations

Quantum simulations allow us that instead of having to model a system mathematically in order to study simulations on it, we can model the system directly with another system.

Quantum simulation has so far been applied mainly to problems in solid state physics, drawing analogies between a qubit lattice and other lattices (of atoms, spins, etc.) such as those studied in this branch of physics. In particular, work has been done on simulations of the Hubbard model, spin Hamiltonians, quantum phase transitions, disordered or frustrated systems (including spin glasses, superconductors, metamaterials and systems exhibiting topological order).

Lucía Absalom Bautista and Spyridanus Andreas Siskos.

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