In theory, quantum computers can do anything that a classical computer can. In practice, however, the quantumness in a quantum computer makes it nearly impossible to efficiently run some of the most important classical algorithms.

The traditional grade-school method for multiplication requires n^2 steps, where n is the number of digits of the numbers you’re multiplying. For millennia, mathematicians believed there wasn’t a more efficient approach.

But in 1960 mathematician Anatoly Karatsuba found a faster way. His method involved splitting long numbers into shorter numbers. To multiply two eight-digit numbers, for example, you would first split each into two four-digit numbers, then split each of these into two-digit numbers. You then do some operations on all the two-digit numbers and reconstitute the results into a final product. For multiplication involving large numbers, the Karatsuba method takes far fewer steps than the grade-school method.

When a classical computer runs the Karatsuba method, it deletes information as it goes. For example, after it reconstitutes the two-digit numbers into four-digit numbers, it forgets the two-digit numbers. All it cares about is the four-digit numbers themselves. But quantum computers can’t shed (forget) information.

Quantum computers perform calculations by manipulating “qubits” which are entangled with one another. This entanglement is what gives quantum computers their massive power, but it is the same property that makes (made) it impossible for them to run some algorithms which classical computers can execute with ease. It was only until some years ago that Craig Gidney, a software engineer at Google AI Quantum in Santa Barbara, California, described a quantum version of the Karatsuba algorithm. (1)

Think. Forget. Move on. Think again…

Know everything.

And you will need to forget.

Forget so that you can learn.

So that you know it all.

The path to light, passes through alleys of darkness.

And trusting the light can only lead to darkness, when the Sun sets down.

You need the Moon.

For it is only there, that you can see your eyes reflected…

Upon the silvery calm lake…

Sun breathing fire.

Light reflected on the Moon…

Cold light reflected on water…

Light passing through your eyes.

In the dead of the night,

You realize that you knew the Sun.

Stand still enough…

And you will listen to the cosmos being born…