Arnaldo Gunzi Quantum

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Scott Aaronson, professor at the University of Texas at Austin, is one of the world’s biggest references on Quantum Computing. The following is a summary of his recent lecture on quantum supremacy.

Quantum computing is not about testing all solutions in parallel and taking the best one.

It’s true that superpositions can be created, but eventually you’ll have to see the result, and we can only observe one of these instances at a time.

The only possibility of having a speedup is to exploit the interference phenomenon, to suppress the amplitudes of the results we don’t want.

It’s like a…

The IBM Quantum Challenge Africa is running, beginning today.

Attend at

Quantum computing is a hot topic, and it has developed a lot in recent years.

Below are some very good books, videos and links.

A very didactic introduction

Quantum computer for high school is an easy introduction (

Applications are now open for the IBM Quantum Challenge Africa 2021. People from all over the world can participate, and the organizers are asking to spread the word, especially to those who have a strong relationship with Africa.

Quantum computing is a rising branch of computing, and it can be disruptive in the near future.

IBM provides the world’s first certification in the field: the Qiskit developer certicate. Qiskit is the quantum computing language for simulating circuits and running on real IBM computers.

See links below.

I just got certified in August 2021. Here are some tips.

About study sources

I’ve been studying quantum computing for a couple of years. The theory can be seen in books like the ones listed in the link below.

About the Qiskit language, the best source comes from IBM…

The famous Bell state is the simplest example of quantum entanglement, where two qubits are intertwined until decoherence separates them. If one is measured as zero, so is the other, if one is measured as 1, so is the other. However, we do not know which of the states will be measured.

The circuit to create the Bell state (|00> + |11>)/sqr(2) is shown below. It uses only a Hadamard and a controlled X.

The GHZ state is similar, for three qubits: (|000> + |111>)/sqr(2). In terms of circuit, it has one more qubit, and one more CX.


The barrier, in qiskit, draws a small line separating circuits.

I always thought that the barrier was just something visual, that it didn’t change anything in the circuit.

However, in fact, the barrier serves to give an instruction to the transpiler: don’t simplify the circuit in the separating barriers.

The simplest example is two H gates in series. The H applied twice equals identity, the effects cancel out. The transpiler simply ignores the two H gates and continues the circuit.

When we put a barrier between the Hs, the transpiler is forced to consider the two H operations. The reason for this? To measure the effect of some noise introduced by gates, for example.

Among the countless logic gates that exists in quantum computing, there are some that have a name — and there was a professor of mine who said, every theorem or tool that deserves a name is important.

I’m going to focus here on the Z, S and T gates, to link with the rotations in Bloch’s sphere.

The Z gate is the best known, it is one of the Pauli matrices, and concerns the rotation around the Z axis.

It transforms the point [1, 1]/sqrt(2) into [1, -1]/sqrt(2). …

Arnaldo Gunzi Quantum

Quantum computing and information

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