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- daveloweRegistered
- University or Employer: Loughborough
- Country: UK
- Occupation: Mature student

@daveloweHi @quan – yes you are quite correct about photons not being interactive – they are very ‘inert’.

There is an architecture based on photons known as the ‘linear optical quantum computer’. These fall into two major sub-types called ‘KLM protocol’ and ‘boson sampling’. Wikipedia has a good article that summarizes what these are.

In either case, the photon is used as the physical qubit, and there are three major ways that information can be encoded into them.

1 .time-bin encoding where the 0 & 1 basis states are ‘early and ‘late’ arrival of a photon; the 2-state quantum mechanical system is ‘time of arrival’

2. number of photos encoding where the 0 & 1 basis states are ‘no photon’ and ‘single photon’; the 2-state quantum mechanical system is the ‘Fock state’

3. polarization where the 0 & 1 basis states are ‘horizontal’ and ‘vertical’; the 2-state quantum mechanical system is ‘polarisation’These types of hardware can be simple to implement since some just rely on simple optical experimental hardware such as mirrors and beamsplitters. The major downside is the velocity of the photons which means that whatever computation you are wanting to perform needs to be performed in one go. Other hardware implementations, such as trapped ion for example, use the internal state of an atom as a qubit, and these can be trapped in one physical location pretty much indefinitely. Unfortunately the quantum information degrades over time through a process known as decoherence.

One interesting crossover design is the CQED or cavity quantum electrodynamics computers where the qubit is an atom trapped in a small mirrored cavity where it can undergo what is known as a Rabi oscillation. This means that the atom energy spontaneously decays and emits a photon which has the qubit information, but this is bounced off a mirror and reabsorbed by the atom and then this process repeats. You can see then that this type of design acts as an interface between trapped atoms and photons.

So far as I’m aware, no large company is actively building an optical quantum computer but I would like to be proven wrong!

- This reply was modified 1 year, 2 months ago by davelowe.

12 August 2020 at 10:10 am in reply to: A First Introduction to Quantum Computing and Information #22861daveloweRegistered- University or Employer: Loughborough
- Country: UK
- Occupation: Mature student

@davelowedaveloweRegistered- University or Employer: Loughborough
- Country: UK
- Occupation: Mature student

@daveloweRegistered- University or Employer: Loughborough
- Country: UK
- Occupation: Mature student

@daveloweRegistered- University or Employer: Loughborough
- Country: UK
- Occupation: Mature student

@davelowehttp://www.optical-lattice.com/ is also a good starting point.

Registered- University or Employer: Loughborough
- Country: UK
- Occupation: Mature student

@davelowe21 May 2020 at 1:36 pm in reply to: Bose-Einstein condensation / Lev Pitaevskii, Sandro Stringari. #3160Registered- University or Employer: Loughborough
- Country: UK
- Occupation: Mature student

@daveloweRegistered- University or Employer: Loughborough
- Country: UK
- Occupation: Mature student

@daveloweThese are the categories that match “quantum”:

Hardware Emerging technologies Quantum technologies

Hardware Emerging technologies Quantum technologies Single electron devices

Hardware Emerging technologies Quantum technologies Tunneling devices

Hardware Emerging technologies Quantum technologies Quantum computation

Hardware Emerging technologies Quantum technologies Quantum computation Quantum communication and cryptography

Hardware Emerging technologies Quantum technologies Quantum computation Quantum error correction and fault tolerance

Hardware Emerging technologies Quantum technologies Quantum dots and cellular automata

Computing methodologies Modeling and simulation Simulation types and techniques Quantum mechanic simulation

Theory of computation Computational complexity and cryptography Quantum complexity theory

Theory of computation Models of computation Quantum computation theory

Theory of computation Models of computation Quantum computation theory Quantum complexity theory

Theory of computation Models of computation Quantum computation theory Quantum communication complexity

Theory of computation Models of computation Quantum computation theory Quantum query complexity

Theory of computation Models of computation Quantum computation theory Quantum information theory

Computer systems organization Architectures Other architectures Quantum computingRegistered- University or Employer: Loughborough
- Country: UK
- Occupation: Mature student

@davelowe~~PDF of the various categories derived directly from the original webpages.~~This is superseded. See the interactive HTML link instead.

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