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Profile William Rothamel
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Message 1729145 - Posted: 26 Sep 2015, 14:18:20 UTC - in response to Message 1729125.  
Last modified: 26 Sep 2015, 14:19:39 UTC

What particle was used? How did they know which one was the partner? How did they sync their clocks to measure the times.

Please describe what is meant by a "quantum internet" and how it would work.

While you are at it, enlighten us on how a quantum computer would work and why it is better than what we have today in sophisticated chip and computer architecture.
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Message 1729157 - Posted: 26 Sep 2015, 15:01:40 UTC - in response to Message 1729145.  
Last modified: 26 Sep 2015, 15:04:09 UTC

That was many question William.
What particle was used? How did they know which one was the partner? How did they sync their clocks to measure the times.

It was photons.
Please describe what is meant by a "quantum internet" and how it would work.

Quantum computers works with qubits instead of bits.
That make Quantum Computers "QC" ideal to factorize integers.
While you are at it, enlighten us on how a quantum computer would work and why it is better than what we have today in sophisticated chip and computer architecture.

I let Seth LLoyd answer to that:)
https://www.youtube.com/watch?v=wkBPp9UovVU


Here is Mr QM AKA Anton Zeilenger:)
http://vcq.quantum.at/research/people/details/14-anton-zeilinger.html

And here is Mr QC AKA Seth LLoyd:)
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Message 1729158 - Posted: 26 Sep 2015, 15:17:43 UTC
Last modified: 26 Sep 2015, 15:38:08 UTC

So far a quantum computers des not exist, although D-Wave has sold a couple of them, but there is a strong doubt about them being real quantum computesr. AFAIK Anton Zeilinger has succeded in teleporting photons up to 143 km (see the Zeilinger Bibliography). A team of Italian scientists has teleported photons to an orbiting satellite, via optics. Maybe this last priority regards only photons teleported via fiber.
Tullio
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Message 1729171 - Posted: 26 Sep 2015, 15:59:32 UTC - in response to Message 1729158.  

So far a quantum computers des not exist, although D-Wave has sold a couple of them, but there is a strong doubt about them being real quantum computesr. Tullio

AFAIK the D-Wave computers only use the method not the technology of QM.
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Message 1729174 - Posted: 26 Sep 2015, 16:09:48 UTC - in response to Message 1729171.  

They use a cryogenic chip developed by them and a kind of ground state search also developed by them. It is is more an analogic coprocessor than a quantum computer.
Tullio
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Message 1729737 - Posted: 28 Sep 2015, 8:26:27 UTC

"Scotty, they beamed some photons 100km away!"
"How primitive...we can show them how it's done."
:D LoL

non-profit org. Play4Life in Zagreb, Croatia, EU
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Message 1729778 - Posted: 28 Sep 2015, 13:31:58 UTC - in response to Message 1729737.  
Last modified: 28 Sep 2015, 14:21:55 UTC

We all know what Q-bits are--I think--. Explain how they are ideal for factoring and how this could be done more expeditiously than a super-computer using two-state logic. Can you write a program to add 2 and 2 in qubit logic.

How do you represent a 2 ?
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Message 1729792 - Posted: 28 Sep 2015, 14:47:26 UTC - in response to Message 1729778.  
Last modified: 28 Sep 2015, 14:57:04 UTC

We all know what Q-bits are--I think--. Explain how they are ideal for factoring and how this could be done more expeditiously than a super-computer using two-state logic. Can you write a program to add 2 and 2 in qubit logic.

How do you represent a 2 ?

You need to be able to use Dirac—or "bra–ket" notation to do that.
But here are some links.
https://en.wikipedia.org/wiki/Shor%27s_algorithm
Here is a lot how it works.
Basic concepts in quantum computation.
http://www.quantiki.org/wiki/Basic_concepts_in_quantum_computation
Qubit Physical representation
https://en.wikipedia.org/wiki/Qubit#Physical_representation
The arithmatic reminds of complex number.
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Message 1729794 - Posted: 28 Sep 2015, 14:53:13 UTC - in response to Message 1729778.  
Last modified: 28 Sep 2015, 14:53:48 UTC

A qubit can represent two states. 2 qbits repersent 4 states, 3 qubits 8 states, 4 qubits 16 states, 5 qubits 32 states and so on. Th problem is when you want to read the answer of a calculation. You must collapse a kind of wavefunction to a number.So far real quantum computers have factored 8 qubits and no more.
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Message 1729798 - Posted: 28 Sep 2015, 15:03:19 UTC - in response to Message 1729794.  
Last modified: 28 Sep 2015, 15:10:19 UTC

A qubit can represent two states. 2 qbits repersent 4 states, 3 qubits 8 states, 4 qubits 16 states, 5 qubits 32 states and so on. Th problem is when you want to read the answer of a calculation. You must collapse a kind of wavefunction to a number.So far real quantum computers have factored 8 qubits and no more.
Tullio

The wave function is called superposition that means you can have both states at the same time.
Quantum superposition is a fundamental principle of quantum mechanics. It states that much like waves in classical physics, any two (or more) quantum states can be added together ("superposed") and the result will be another valid quantum state; and conversely, that every quantum state can be represented as a sum of two or more other distinct states. Mathematically, it refers to a property of solutions to the Schrödinger equation; since the Schrödinger equation is linear, any linear combination of solutions will also be a solution.
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Message 1729832 - Posted: 28 Sep 2015, 17:03:37 UTC - in response to Message 1729798.  
Last modified: 28 Sep 2015, 17:09:43 UTC

Transistor logic (Binary) has two states. Qubits have three states do they not.

If I want to add 2 and 2 on a digital computer I represent the numbers two by

.....010 in registers. I then examine:

.....010
.....010
with an adder (Boolean Exclusive OR plus Boolean AND) and a carry function and I would get

.....100 with a 0 carry to the fourth position

The logic circuit for the last three bits of the adding register would look as shown below with carry in and carry out.



The three blocks are Full Adders whose logic circuit configurations are well known

so like I said help me understand by showing how you would do this on a quantum computer.
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Message 1729838 - Posted: 28 Sep 2015, 17:31:51 UTC - in response to Message 1729832.  
Last modified: 28 Sep 2015, 18:13:11 UTC

Addition 2+2=4 with qubit bar-ket notation.

|2>
|2>
------
|4>

Quantum register of size three can store individual numbers such as 3 or 7,
but, it can also store the two of them simultaneously.

=> 1 / square(2) * (|3> + |7>)

In fact we can prepare this register in a superposition of all eight numbers -- it is enough to put each qubit into the superposition.
|0> + |1> + |2> + |3> + |4> + |5> + |6> + |7>
ignoring the normalisation constant 1 / square(2)
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Message 1729858 - Posted: 28 Sep 2015, 18:14:56 UTC - in response to Message 1729838.  
Last modified: 28 Sep 2015, 18:18:13 UTC

Still not seeing the logic involved nor the physical circuit. To start with: What are the states of a Qubit ? is it yes, no, maybe or 0, 1, and ? do we use base three here ?

Do we have Quantum: Logic, Venn Diagrams, Karnaugh maps??
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Message 1729862 - Posted: 28 Sep 2015, 18:29:13 UTC - in response to Message 1729858.  
Last modified: 28 Sep 2015, 18:37:59 UTC

Still not seeing the logic involved nor the physical circuit. To start with: What are the states of a Qubit ? is it yes, no, maybe or 0, 1, and ? do we use base three here ?

Qbits and bits can only have two states.
But a qubit can also have a superposition so one qubit can have two states at the same time.
Tullio explained that.

And you can use any base you want. I prefer decimal. Or hexadecimal.
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Message 1730052 - Posted: 29 Sep 2015, 12:28:08 UTC
Last modified: 29 Sep 2015, 12:29:15 UTC

Quantum computers are nt built to do things that digital computers do well. A typical problem is that of factoring a huge number. Take two large primes, multiply them and you get a huge number which is not prime. To factorize it you can try the Eratothenes sieve method, used for searching prime numbers. You divide it by 2, then by three, then by 5 and so on. This takes a vry long time. A quantum computer should need only a single division.
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Message 1730059 - Posted: 29 Sep 2015, 13:00:54 UTC
Last modified: 29 Sep 2015, 13:04:45 UTC

Until now in factoring numbers using quantum computers only have found 15, 21, 143 and 56153.
http://phys.org/news/2014-11-largest-factored-quantum-device.html
"We're still a far way from outperforming classical computers," Dattani told Phys.org. "The highest RSA number factored on a classical computer was RSA-768, which has 768 bits, and took two years to compute (from 2007 to 2009)."
RSA numbers are a set of large "semiprimes"—numbers with exactly two prime factors. RSA numbers are particularly special due to the difficulty in factoring them. For this reason, they are used by governments, militaries, and banks to keep financial information secure.
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Message 1730062 - Posted: 29 Sep 2015, 13:06:59 UTC - in response to Message 1730059.  
Last modified: 29 Sep 2015, 13:07:28 UTC

I've read on "Nature" that cryptographers in banks and military institutions are worried about quantum computers ability in factorizing numbers, since security of RSA and other cryptographyc methods are based upon the assumption that very large numbers are difficult to factorize. If this is no longer true, they should adopt other methods, which are being studied. On the other hand, quantum criptography has already been used in Swiss cantonal elections to safely distribute cryptographic keys.
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Message 1730064 - Posted: 29 Sep 2015, 13:15:32 UTC - in response to Message 1730062.  
Last modified: 29 Sep 2015, 13:19:03 UTC

But is it not the reason to use quantum computers only about distribute cryptographic keys.
From what I have heard that Eve cannot evesdrop on quantum keys/messages without Alice and Bob knows that.
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Message 1730065 - Posted: 29 Sep 2015, 13:23:10 UTC - in response to Message 1730064.  

This is the only practical application so far. The rest lies in the future.
Tullio
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Message 1730087 - Posted: 29 Sep 2015, 14:07:53 UTC

Still would like to know why so called quantum computers are good at factoring and exactly why and how the "circuitry" and logic works.
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