I’m either seeing unexpected behavior, or doing something wrong (probably doing something wrong).

If I run the following on Google’s Quantum Playground…

>>>>>>>>>>>>>>>>>>>>>>>>>>>

VectorSize 8

SigmaX 0

Hadamard 0

Hadamard 1

CNot 0,1

Hadamard 0

Hadamard 1

MeasureBit 1

print measured_value

<<<<<<<<<<<<<<<<<<<<<<<<<<<

I expect to see a non-zero measured_value. When I run this in the playground by stepping through the program, the CNot has no affect on the qubit. What am I doing wrong?

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I’m working on a science fiction project that includes an important episode of quantum hacking . I need a slightly more realistic framework in order to fill in the story, and I’m hoping you can help me answer a few questions. I apologize in advance if my questions are elementary to the point of being annoying, but I’m hoping some of you experts can help me out.

Let’s assume there is a spaceship whose navigational decisions are protected by quantum encryption, using a series of optical channels. Based on what I’ve seen and read, including the stuff discussed on Youtube by Vadim Makarov, it would very much be possible to hack such a system and change the outcome.

According to Mr. Makarov (and others, I’m sure), you could fire a pulse into the channel and use back-reflection to built a map of the quantum state without disturbing it. From there, you could manipulate it.

My questions are:

1. How would the hacking computer “connect” to the system’s optical channel? Would a cable have to be coupled to the optical channel, and what would this look like? (My guess is ‘yes’, since photons would have to be injected and collected).

2. Is there a conceivable way for the location of the device to be discovered while said device is in operation? (electricity, I’m sure – but anything else?)

3. How would the device be uncoupled/removed? Would this even matter, if the hacking operation had achieved its desired result? Would you have to cover up the hole you made?

4. What are some rare materials involved in the building of a quantum hacking device?

5. Which components of a quantum hacking device do you think would be most difficult to manufacture?

Any bits of insight you could provide would be very much appreciated! Thanks for taking the time to read my questions.

Best wishes,

arrowhead

p.s. if you know of a better forum or person to ask these questions, please do let me know.

]]>A CNOT gate would only flip 1 of the bits. I need |11> -> |00> purely, without any outside entanglement with a third qbit.

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My thinking is, for such a scenario to be supported, you’d need to have a generic algorithm for sequentially eliciting the linear combinations that have raised probability amplitudes in a series of rounds. Simply doing measurement in each basis isn’t enough, because you don’t want to either treat each qubit as an individual or enumerate the potentially spaces between linear combinations. Therefore, for example, you want to run the algorithm, and read the ith linear combination with very high probability, regrouping the probability amplitude for any other linear combination with raised probability to that item.

By repeatedly running the algorithm, and simply iterating until either an already seen linear combination is witnessed, or some moniker, such as the zero vector, is read, you can get all possible results.

Does such an algorithm already exist? If so, what is it’s name?

]]>From the point of a VC, should quantum computing be of interest NOW for investment?

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Am I correct in thinking that post-quantum cryptography such as lattice based solutions are designed to run on classical computers but be resistant to quantum attacks, whereas quantum cryptography such as BB84 is designed to run on quantum computers to communicate between them? Thanks.

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