In my constant thrill to know more about Quantum Computing I wanna know what is this relation. Additionally: Can one use squeezed light to effect multi-qubit operations on single photon qubits, or are these completely independent approaches?


1 Answer 1


By photon qubits, I'm assuming that you meant single-photon qubit systems.

Can one use squeezed light to effect multi-qubit operations on photon qubits, or are these completely independent approaches?

There are two protocols in quantum communication namely, discrete-varibale (dv) and continuous variable (cv). Squeezed light qubits are a part of cv quantum communication protocols because continuous-variable entanglement can be efficiently produced using squeezed light. Whereas single-photon qubits are part of the dv protocols. So to answer your question, they are both different approaches.

The main difference between these protocols is explained in this review paper "Quantum information with continuous variables":

A valuable feature of quantum optical implementations based upon continuous variables, related to their high efficiency, is their 'unconditionalness'. Quantum resources such as entangled states emerge from the nonlinear optical interaction of a laser with a crystal in an unconditional fashion. This 'unconditionalness' is hard to obtain in dv qubit-based implementations based on single-photon states.

To expand on the answer, Splitting squeezed light on beam splitter results in two output beams in an entangled state. The quality of this entanglement produced leads to imperfect communication, where the degree of imperfection depends on the amount of squeezing of the laser light involved.

For example, in a realistic quantum key distribution scenario, the cv states accumulate noise and emerge at the receiver as contaminated versions of the sender’s input states. The dv quantum information encoded in single-photon states is reliably conveyed for each photon that is not absorbed during transmission.

I hope that this cleared your question.

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    $\begingroup$ Note that both discrete and continuous variables are possible approaches to optical computing as well as communication $\endgroup$
    – Mithrandir24601
    Commented Apr 15, 2018 at 19:05
  • $\begingroup$ I am not an expert, but this certainly has helped me know more about the topic. Thanks a lot! $\endgroup$ Commented Apr 16, 2018 at 9:25

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