# Tag Info

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A comment said that the most common way to encode q information in photons is using their internal degrees of freedom, not using a "there/not there" encoding. When using photons, quantum information can indeed be encoded into an internal degree of freedom; for instance the polarization of the photon. However, there are plenty of other systems where the ...

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The idea of squeezing arises when discussing the state of a quantum harmonic oscillator (e.g. a bosonic system). Such systems differ from simpler qudit systems in that, even when only a single mode is being considered, the system is infinitely dimensional. A common way to describe these systems is via pairs of non-commuting observables, often the "position" ...

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You are right, photonic systems are described by an infinite (separable) Hilbert space---the bosonic Fock space---and their formalism makes extensive use of infinite values, both countable and uncountable. The quantum computing paradigm based on this Hilbert space is called continuous-variable (CV) quantum computing, and a lot of different protocols and ...

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Here is a handful of Linear Optical Quantum Computation (LOQC) resources I have found useful in the past: "Linear Optical Quantum Computing" (2005) by Kok et. al.: this is probably the best review paper that came out after Knill, Laflamme, and Milburn's 2001 discovery that theoretically-efficient LOQC was possible. It's a pretty thorough but very accessible ...

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a good stater i would say is the paper of Knill and Laflamme about LOQC (Linear Optical Quantum computing) from 2001, that says that quantum computing can be achieved with linear optic. Photons are really good as they can be used in many way to create qubits (polarisation of course, but also time, frequency, OAM). A Ph.D Thesis of Laurent Olislager is ...

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Your understanding is correct. In the theory of photon polarization, the parametrization of the Bloch sphere (or its surfave) has traditionally another name. On the wikipedia page for the Jones calculus (the parametrization of the Bloch sphere surface), you'll find a table for the correspondence between kets and polarizations. To summarize, eigenstates ...

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As for any platform, one has to choose a suitable $d$-dimensional "computational" subspace. Suitability depends on your application, but generally it means that one should be able to perform operations on that subspace and couple it to other qudits. In practice, these operations will couple the qudit to degrees of freedom outside of the subspace ...

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You start with a polarisation filter. This does nothing to the path of your photon and, effectively, measures the polarisation of the photon, meaning that you prepare the "second" qubit in the fixed state determined by what polarisation the filter is detecting. So, at this point, you have $$|0\rangle|-\rangle$$ Then, you input to a beamsplitter. ...

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Not exactly. You are correct, there is a single photon; qubit 1 is its path, qubit 2 is its polarization. The waveplates implement an oracle (one from 4 possible). You are wrong about the beam splitters; beam splitters do not affect polarization, so they act on the qubit 1 only as Hadamard gates. The $|-\rangle$ state of qubit 2 is created by the ...

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I see the heart of your question. I'd like to clarify a bit, before answering your question though. Matrices (aka operators) do not measure quantum states--they operate on them. Specifically, they project the state into the matrix's eigenvectors. We can then measure that projected state in a particular basis that may be the same or different than what the ...

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Intraphoton entanglement uses the degrees of freedom from one photon only to create entanglement. So, here either polarization and linear momentum or polarization and angular momentum can be used to create entanglement. Interphoton entanglement is the entanglement created between 2 spatially separated photons. So, naturally latter is less stable than former. ...

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