Message boards :
Science (non-SETI) :
Interesting Physics

Message board moderation

Previous · 1 · 2 · 3 · **4** · 5 · 6 · 7 . . . 20 · Next

Author | Message |
---|---|

William Rothamel Send message Joined: 25 Oct 06 Posts: 3507 Credit: 1,546,701 RAC: 1,233 |
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. |

janneseti Send message Joined: 14 Oct 09 Posts: 14106 Credit: 655,366 RAC: 0 |
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:) |

tullio Send message Joined: 9 Apr 04 Posts: 7283 Credit: 2,276,599 RAC: 2,380 |
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 |

janneseti Send message Joined: 14 Oct 09 Posts: 14106 Credit: 655,366 RAC: 0 |
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. |

tullio Send message Joined: 9 Apr 04 Posts: 7283 Credit: 2,276,599 RAC: 2,380 |
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 |

KLiK Send message Joined: 31 Mar 14 Posts: 1296 Credit: 14,838,306 RAC: 17,368 |
"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 |

William Rothamel Send message Joined: 25 Oct 06 Posts: 3507 Credit: 1,546,701 RAC: 1,233 |
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 ? |

janneseti Send message Joined: 14 Oct 09 Posts: 14106 Credit: 655,366 RAC: 0 |
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. 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. |

tullio Send message Joined: 9 Apr 04 Posts: 7283 Credit: 2,276,599 RAC: 2,380 |
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 |

janneseti Send message Joined: 14 Oct 09 Posts: 14106 Credit: 655,366 RAC: 0 |
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. 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. |

William Rothamel Send message Joined: 25 Oct 06 Posts: 3507 Credit: 1,546,701 RAC: 1,233 |
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. |

janneseti Send message Joined: 14 Oct 09 Posts: 14106 Credit: 655,366 RAC: 0 |
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) |

William Rothamel Send message Joined: 25 Oct 06 Posts: 3507 Credit: 1,546,701 RAC: 1,233 |
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?? |

janneseti Send message Joined: 14 Oct 09 Posts: 14106 Credit: 655,366 RAC: 0 |
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. |

tullio Send message Joined: 9 Apr 04 Posts: 7283 Credit: 2,276,599 RAC: 2,380 |
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. Tullio |

janneseti Send message Joined: 14 Oct 09 Posts: 14106 Credit: 655,366 RAC: 0 |
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. |

tullio Send message Joined: 9 Apr 04 Posts: 7283 Credit: 2,276,599 RAC: 2,380 |
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. Tullio |

janneseti Send message Joined: 14 Oct 09 Posts: 14106 Credit: 655,366 RAC: 0 |
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. |

tullio Send message Joined: 9 Apr 04 Posts: 7283 Credit: 2,276,599 RAC: 2,380 |
This is the only practical application so far. The rest lies in the future. Tullio |

William Rothamel Send message Joined: 25 Oct 06 Posts: 3507 Credit: 1,546,701 RAC: 1,233 |
Still would like to know why so called quantum computers are good at factoring and exactly why and how the "circuitry" and logic works. |

©2019 University of California

SETI@home and Astropulse are funded by grants from the National Science Foundation, NASA, and donations from SETI@home volunteers. AstroPulse is funded in part by the NSF through grant AST-0307956.