10

What you call a black box is simply isolating the quantum system that stores (or represents) your qubits from the environment. This can be done in several ways depending on your physical realization. For example, in an ion trap based quantum computer, one uses states of a single ion to represent a qubit, and isolates that from the environment by levitating ...


10

In summary, no. If you think about it, this makes sense. When measuring a quantum system with $n$ qubits, you get $n$ bits of information. the $2^n$ figure exists only when the system is in superposition, which a classical computer cannot access. The specific theorem in question here is Holevo's theorem. To quote Wikipedia: In essence, the Holevo bound ...


7

A good summary on the current state of QRAM (as of 2017) can be found in this paper, and a comparison of it with classical methods can be found in this talk. The Giovannetti type "bucket brigade" QRAM still seems to be the best that is known, although modifications exist. There are serious caveats to the use of any such QRAM, and no alternative that avoids ...


6

This is discussed in chapter 5 of Ciliberto et al.. The purpose of most quantum(-enhanced) machine learning algorithms is to speed-up the processing of classical data over what is possible with classical machine learning algorithms. In other words, the context is that you have a set of classical vectors $\{\boldsymbol x_k\}_k$, and you want to compute some ...


4

They say that this scheme requires to throw $O(N)$ switches for each memory call, but I don't understand why is this the case. From the above, it would seem that one just needs to throw $O(\log_2(N))$ switches, one per bifurcation, to get from the top to the bottom. It seems to me that $n= \log_2 N$ is the length of the address register: the number of ...


3

It's not so much a matter of big data, but that of saving data. Quantum storage is still (much like the rest of the field) in its infancy. (Take what I write with a grain of salt. It's likely to change rapidly.) There are a few theories on how quantum computers might be able to hold "memory". One of these is using nuclear spin. E.g. using long-lived ...


3

Unfortunately the state of the technology regarding memories is not as developed as you seem to expect. When we talk about a memory, we think of a device that can store information for an infinite amount of time (for all practical purposes). So before we can think about the size of the memory in a quantum computer, we should look at whether a single quantum ...


3

Yes, you can encode a program into your qubits in exactly the same way you'd encode a program into bits and then run circuits that interpret the program. One might hope that you could encode the program in some fancy exponentially efficient way, but in Mike&Ike they prove that's not possible. Because there's no exponential advantage, and because the ...


2

You seem to be thinking about "quantum memory" like it is one specific thing and there is only one specific way it can happen. In reality, what you describe is a valid notion of quantum memory. Another popular one, involving the element Yb, is this one: https://arxiv.org/abs/1701.04195.


2

An answer to this question seems to have been given by the same authors, in a different follow-up paper which I hadn't seen before. In [1], the authors write (emphasis mine): A classical RAM that uses the bucket-brigade addressing schemes need only activate $O(n)$ transistors in the course of a memory call, in contrast with a conventional RAM that ...


2

Your question revolves implicitly around the concept of quantum decoherence and how to protect real-world implementations of qubits from it for a long time. This is an incredibly general problem, and at the same time, the details are wildly dependent on the technology used. If you have access to it, you can check chapter 5 : "Noise and decoherence" of ...


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