3 ms·

> “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

> “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?

albertgoeswoof 8y ago
I thought qubits had an infinite range of states?
- tzakrajs 8y ago
  Oh yeah, thats right.. Isn't it based on orientation in a spherical sense? I guess you could have an infinite number of those orientations.
  - whatshisface 8y ago
    A pure quantum state is a basis vector, written like |n>. It's called a basis vector because it shares a list of mathematical properties with the x̂,ŷ,ẑ coordinate basis vectors you might be familiar with. They can be combined, (like coordinate vectors) by writing coefficients before them. For example, 1/√2 |a> + 1/√2 |b> would be a combination of state a and state b. Combinations of states obey the condition that the sum of the squares of each coefficient equals one. This is the unitary constraint, and above you can see that 1/√2^2 + 1/√2^2 = 1/2 + 1/2 = 1. Coefficients can be complex numbers, which consist of a real part and an imaginary part. So, putting all of this together, a qbit that may be in the state |1> or the state |0> may also be in the state (a+bi)|1> + (c+di)|0>. With the unitary constraint, we can cut out a degree of freedom by introducing the equation |a+bi|^2 + |c+di|^2 = 1. This leaves three degrees of freedom, which can be mapped in to a sphere by a change of coordinates. Three spherical coordinates plus the unitary constraint specifies the four-number state combination.
    - tzakrajs 8y ago
      Very insightful, thank you!
barbegal 8y ago
It's a confusing quote. They have achieved 18 qubits from 6 photons. But 18 qubits can store more information than 18 regular bits however when the 6 photon system is measured the quantum state collapses to 18 bits of data. 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.
- 21 8y ago
  Even in traditional memory, you can use a single degree of freedom to store multiple bits, by quantizing the charge. Like in TLC flash memory, where you can store 3 bit per cell. This is because in traditional memory, a single "cell" stores many elementary charges (electrons).
jxy 8y ago
There are 18 qubits stored in 6 photons, where each photon effectively have 3 qubits from its 3 different degrees of freedom. Reading the arxiv document prepared by Microsoft Word is so painful. Can't Microsoft learn something from TeX?

albertgoeswoof 8y ago

I thought qubits had an infinite range of states?

tzakrajs 8y ago
Oh yeah, thats right.. Isn't it based on orientation in a spherical sense? I guess you could have an infinite number of those orientations.
- whatshisface 8y ago
  A pure quantum state is a basis vector, written like |n>. It's called a basis vector because it shares a list of mathematical properties with the x̂,ŷ,ẑ coordinate basis vectors you might be familiar with. They can be combined, (like coordinate vectors) by writing coefficients before them. For example, 1/√2 |a> + 1/√2 |b> would be a combination of state a and state b. Combinations of states obey the condition that the sum of the squares of each coefficient equals one. This is the unitary constraint, and above you can see that 1/√2^2 + 1/√2^2 = 1/2 + 1/2 = 1. Coefficients can be complex numbers, which consist of a real part and an imaginary part. So, putting all of this together, a qbit that may be in the state |1> or the state |0> may also be in the state (a+bi)|1> + (c+di)|0>. With the unitary constraint, we can cut out a degree of freedom by introducing the equation |a+bi|^2 + |c+di|^2 = 1. This leaves three degrees of freedom, which can be mapped in to a sphere by a change of coordinates. Three spherical coordinates plus the unitary constraint specifies the four-number state combination.
  - tzakrajs 8y ago
    Very insightful, thank you!

barbegal 8y ago

It's a confusing quote. They have achieved 18 qubits from 6 photons. But 18 qubits can store more information than 18 regular bits however when the 6 photon system is measured the quantum state collapses to 18 bits of data. 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.

21 8y ago
Even in traditional memory, you can use a single degree of freedom to store multiple bits, by quantizing the charge. Like in TLC flash memory, where you can store 3 bit per cell. This is because in traditional memory, a single "cell" stores many elementary charges (electrons).

jxy 8y ago

There are 18 qubits stored in 6 photons, where each photon effectively have 3 qubits from its 3 different degrees of freedom. Reading the arxiv document prepared by Microsoft Word is so painful. Can't Microsoft learn something from TeX?