41–50 of 152 posts
> “It’s as though you took six bits in your computer, but each bit tripled in how much information it could hold,” Schreppler said "Each bit is tripled in how much information it could hold"? Normally bits have two states, but Shreppler is claiming these qubits can have six states? What am I missing?
Even neater is that they are using quantum entanglement in radar to detect stealth planes: https://www.popsci.com/china-quantum-radar-detects-stealth-p...
Yea, you have to explain this. It made no sense when I first read it, and it still makes no sense. Here is how radar works: You shine a flashlight somewhere. If there is an object within range, some of the light is reflected back at you and you know there is an object. This is literally what radar does. So, what part of this, and how, does this "quantum" magic affect?
When the reflection returns, they can use the entanglement to sort out signal from noise much better and radar is safe from jamming and spoofing.
> “It’s as though you took six bits in your computer, but each bit tripled in how much information it could hold,” Schreppler said "Each bit is tripled in how much information it could hold"? Normally bits have two states, but Shreppler is claiming these qubits can have six states? What am I missing?
I thought qubits had an infinite range of states?
Question: Why superfluid 4He is not quantum-entangled? What differentiates macroscopic many-body quantum states from many-body quantum entanglement?
Superfluid 4He is quantum-entangled and non-local effects are observable. https://www.sciencedaily.com/releases/2017/03/170321110344.h...
You can have flasks of superfluid 4He with thousands of moles of entangled atoms clearly visible.
> “It’s as though you took six bits in your computer, but each bit tripled in how much information it could hold,” Schreppler said "Each bit is tripled in how much information it could hold"? Normally bits have two states, but Shreppler is claiming these qubits can have six states? What am I missing?
How do you get 18 qubits from 6 photons? You use multiple degrees of freedom. Whereas a bit in traditional memory has a single degree of freedom (electric charge), photons have many degrees of freedom such as polarity, direction of travel and angular momentum.
> “It’s as though you took six bits in your computer, but each bit tripled in how much information it could hold,” Schreppler said "Each bit is tripled in how much information it could hold"? Normally bits have two states, but Shreppler is claiming these qubits can have six states? What am I missing?
Reading the arxiv document prepared by Microsoft Word is so painful. Can't Microsoft learn something from TeX?
Earlier quoted context omitted.
Yea, you have to explain this. It made no sense when I first read it, and it still makes no sense. Here is how radar works: You shine a flashlight somewhere. If there is an object within range, some of the light is reflected back at you and you know there is an object. This is literally what radar does. So, what part of this, and how, does this "quantum" magic affect?
It works like normal radar, except that they send one entangled photon towards the plane and keep the other. When the reflection returns, they can use the entanglement to sort out signal from noise much better and radar is safe from jamming and spoofing.
Originally "We 'shine' a bunch of photons at an object, and see if they come back. Except there could be dragged decoy spamming photons back at us, and we don't know if there is. Or it could be sending out so much light, our photons coming back are lost in the mix."
With quantum: "We can verify that any photons that get reflected are the ones that we sent out and check only our photons when flooded with photons from enemy flashlights."
Right?
Earlier quoted context omitted.
The part I don't understand is the "spooky action at a distance." Isn't this just the same as if the qbits were already in whatever their final state was as soon as they were entangled? Or in other words, is there any experimental basis for determining that the "cat" stayed alive at all? It seems a lot less magical when we just determine that in fact the value is the same no matter when or where you measure it, altho…
The idea that the qbits choose which value they'll collapse to at time of entanglement is called local hidden variable theory, which John Bell disproved in 1964: https://en.wikipedia.org/wiki/Local_hidden_variable_theory In more practical terms, the theory also falls apart when you start doing more complicated things with entangled qbits than just measuring them, like quantum teleportation or error correction.
I visited USTC several years ago, (2014) and in this time they have basically doubled the number of qubits they can entangle, so this is a great step forward. At around ~100 qubits quantum computing becomes very useful, so maybe we won't have to wait too long.
What's the size needed for cracking large-primes based encryption? If not at 100 qubits, what are some useful calculations that we can do at that size?
Earlier quoted context omitted.
Superfluid 4He is quantum-entangled and non-local effects are observable. https://www.sciencedaily.com/releases/2017/03/170321110344.h...
So why it's not taken into account when quantum-entanglement records are broken? You can have flasks of superfluid 4He with thousands of moles of entangled atoms clearly visible.