Questions tagged [photonics]
It is the branch of physics and engineering concerned with the properties and transmission of photons. Use this tag for those questions about photonics which are relevant to quantum computing.
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Type I fusion Gate
In the type I fusion gate of the Rudolph-Browne protocol,
I fail to understand how the detection of a photon means the entanglement of the two Bell pairs.
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What is complete structures of the photonic quantum computers?
I am interested in studying quantum computers based on photonic integrated circuits. I am looking for a site, article, book, or material that will introduce the process of its implementation step by ...
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What is the optimal hardware for quantum computing, and what factors contribute to its preference?
In conventional computing, the use of CMOS (Complementary Metal Oxide Semiconductor) technology as the foundational circuitry for digital logic gates in CPUs has become the industry norm. CMOS's ...
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What's the difference between Superconductor, Photonics, and Nuclear Magnetic Resonance implementation of the physical QC?
I'm a bit new to Quantum Computing and I wonder why organisations are using different physical architecture.
I realise that any physical implementation can be valid as long as it uses the fundamentals ...
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How to entangle 2 qubits using a polarizing beam splitter?
A polarizing beam splitter splits a continuous beam of photons in 2 directions:
(from here)
(from here)
I am curious and have a few related questions about using simple optics in quantum computing:
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Two-way quantum computers (like in Ising model) - are they possible? Could solve general NP problems? [closed]
Standard one-way quantum computers (1WQC) allow for e.g. Shor, Grover algorithms, however, general NP problems seem too difficult for them(?) - bringing an open question if they could be somehow ...
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Can one simulate Gaussian Boson Sampling using Fock Boson Sampling or vice versa?
In Fock Boson Sampling, one starts with a particle-number state $|n_1, ..., n_m\rangle$ of $m$ modes, sends it to an interferometer effecting a unitary operation $U$ on the creation operators, and ...
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Relation between the output density matrix and the annihilation operators?
The annihilation opertors $\{\hat{a_R}^{(m)}\}_{m=1}^{M}$ of the modes obey the relation
\begin{align}
\label{annihilation}
\hat{a_R}_R^{m}
&= \sqrt{\eta_h} e^{i \phi} \hat{a_S}^{(m)} + \sqrt{1- \...
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Applications of quantum channel's different representations in photonic quantum computing?
We know that quantum channel has different representations, for example, Kraus representation and Stinespring representation. Do these representations have applications in photonic quantum computing ...
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Physical interpretation of a 2-photon-qubit system occupying the antisymmetric Bell state
This question regards the reconciliation of QIT with what I have learned separately in lectures about quantum physics. My understanding is that indistinguishable bosons are always described by ...
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Is there any error correction experimental set-up based on stationary-flying hybrid systems?
In a former question of mine I asked to detail the functioning of a photonic based set-up encoding a quantum state within a Shor code.
I would like to be updated on the eventual existence of any ...
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What are currently the best reported qubit error rates per gate operation?
Based on some investigation, I have found the best qubit coherence timescales, in superconducting architectures, to be the order of milliseconds.
https://journals.aps.org/prb/abstract/10.1103/PhysRevB....
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Are there practical uses for boson sampling?
Boson sampling is a computation that is not doable on classical machines but quite doable on quantum photonic machines.
(https://www.researchgate.net/figure/Experimental-results-for-3-and-4-boson-...
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Simulating light absorption in Photosynthesis through Quantum computing
Basically, I want to simulate the above photosystem process of light absorption. Above is a diagram of laser beams shot into antenna pigment molecules and traveling to the reaction center. Two ...
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CNOT gate path interference
I have a question on paper https://doi.org/10.1038/nature02054.
In this paper, the CNOT gate is realized using a beam displacer for higher stability. The figure below shows a 1:1 mapping from (a) to (...
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What is a "spatially encoded qubit"?
I am studying the photonic CNOT (https://arxiv.org/abs/quant-ph/0403062v1).
I am not understanding what is a spatially encoded qubit?
How the setup in fig. 1(b) can create this spatially encoded qubit?...
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QuTiP lecture: Single-Atom-Lasing
I have tried to run one of the examples in QuTip lectures: single atom lasing.
Although I have used the prepared code represented in reference, I have received error and I have not been able to ...
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Faithful description of a photonic setting with the circuit model
The above picture comes from this paper.
The circuit on the left and the one on the right are equivalent (up to the basis).
However, there is an important difference: the circuit makes the input -- i....
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On the photonic implementation of Shor's code
The above picture comes from this paper.
I can see that the standard Shor's code has been re-designed.
I have two main doubts:
I can't figure out in figure (b) how the setting inputs the state $\...
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Is 216 qumodes photonic quantum processor equivalent to 216 qubits superconducting quantum processor, in terms of computational power?
Xanadu just launched borealis, 216 qumodes photonic quantum computer, this week.
https://xanadu.ai/blog/beating-classical-computers-with-Borealis
Its number of qubits is very interesting because it ...
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Gate times for photonic quantum computers
I am trying to understand the landscape of one- and two-qubit gate times for various quantum computing architectures. It is not so hard to find gate times for various gates such as Hadamard, CNOT and ...
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How big is the Hilbert space of a boson sampling experiment?
Boson sampling experiments are typically characterized by two key parameters: the number of photons $M$ and the number of modes $N$.
A recent experimental demonstration (arXiv:2106.15534) with $M = ...
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Does a photonic quantum computer control a single photon?
Does a photonic quantum computer control a single photon and use it to represent a single qubit?
I think ion trapped quantum computers use a single ion to represent a qubit. I would like to know how a ...
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How are two photons entangled in the Xanadu computer?
I was recently reading about how Xanadu made a scalable, room-temperature-operating quantum computer using photons as qubits (see this link). It said that in the logic gates, it entangles two photons ...
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Understanding polarizing beam splitters
I have been trying to understand this heralded CNOT gate on photons but I have some questions regarding polarizing beam splitters:
The way I understand it, a PBS lets the photon through if the photon ...
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What is an electro-optic switch?
I found an implementation of a CNOT in photonic QC and I just couldn't find any info on a component named "electro-optic switch"
What does it do exactly?
How does it work?
The ...
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What are the most popular QND measurement implementations used in photonic quantum computers?
What components are used in order to perform QND measurement in photonic quantum computers?
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How is measurement performed on a stream of polarized photons?
Is it possible to use a simple laser to measure qubits in optical quantum computers, or is a single-photon emitter absolutely necessary? If you can do it with a simple laser, how would you go about ...
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Optical quantum computers VS Superconducting quantum computers VS Electron-spin quantum computers
One of the main problems of superconducting quantum computers is that it is necessary to maintain a very low temperature (near absolute zero).
Such cooling is very expensive and complex.
Why, then, ...
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Design NISQ Circuit with StrawberryFields
I am trying to design this circuits with strawberry fields. However I could not connect my first and second qubit mode:
orange boxes are beam splitters, blue boxes are phase shifters. The green box ...
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Is Gaussian boson sampling (used for showing quantum advantage) a subcategory of the continuous variable approach?
I read about the photonic QC Jiŭzhāng that showed quantum advantage by Gaussian boson sampling. I read that boson sampling itself is a sub-universal technique of QC (where they use single-photon ...
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How do we realise photonic gates?
I am interested in photonic computing, and I am curious how the gates work. I once saw a picture of a photonic CNOT gate that used just mirrors and polarizers. I have not been able to find any ...
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How are Franson Interferometers used to prove security in Photonic QKD Experiments?
I am currently reading this paper about Quantum Key Distribution Protocols which use Franson Interferometers to secure against eavesdroppers. I am having trouble understanding how the interferometers ...
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Why do we use two optical modes per qubit in the KLM scheme?
The original KLM paper says:
The basic states of a bosonic qubit encoded in modes $l_1$ and $l_2$ are $|0\rangle\mapsto|0\rangle_{l_1}|1\rangle_{l_2}$ and $|1\rangle\mapsto|1\rangle_{l_1}|0\rangle_{...
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How can a half-wave plate affect the position qubit and not the polarization qubit of a photon?
I recently was watching these 2 videos on Coursera which show how to build a simple quantum computer that can implement the simplest case of the Deutsch-Jozsa algorithm (which uses only 2 qubits).
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How do we restrict to a limited number of dimensions, say 3 for qutrits, while using OAM states of light?
When a azimuthal phase $\mathrm{e}^{il\phi}$ is applied to gaussian beams having plane wavefront, they develop a corkscrew sort of structure and therefore possess an orbital angular momentum in ...
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Question about DIY Quantum Computer Prototype
I recently came across these 2 videos on Coursera which show how to build a simple quantum computer that can implement the simplest case of the Deutsch-Jozsa algorithm (which uses only 2 qubits).
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Do photons also suffer from decoherence?
In this Question Why do optical quantum computers not have to be kept near absolute zero while superconducting quantum computers do?
A comment said that the most common way to encode q information in ...
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How do I add 1+1 using a photonic computer?
A similar question has been previously asked & has an excellent answer discussing half, full & ripple carry adders. I am curious to find out how these adders would be constructed in the ...
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What is infinite squeezing?
I am working my through the Strawberry Fields documentation & the section on state teleportation states:
Here, qumodes $q1$ and $q2$ are initially prepared as (the unphysical) infinitely squeezed ...
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What types of quantum systems use infinite values?
Background
I am curious to learn more about any work that has been done regarding quantum systems that deal with infinite values. I am primarily interested in photonic quantum computing; however I am ...
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What are some good resources for learning about photonic qubits?
I am interested in resources that would allow me to learn about the physics behind optical quantum computation, and specifically, the physical properties of photonic qubits. I have some good resources ...
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Are single photons necessary for this quantum autoencoder implementation?
The following diagram is from Experimental Realization of a Quantum Autoencoder: The Compression of Qutrits via Machine Learning
How this setup works:
What will be obtained from this set up is the ...
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What is the difference between "intraphoton" and "interphoton" entanglement?
I am trying to better understand the following:
What is the difference between Intraphoton Entanglement and Interphoton Entanglement?
I am new in this field and i want to proceed some work on ...
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Physical Interpretation of Pauli Matrices as Polarization Check
We know that the Pauli matrices are:
$$\sigma_x = \begin{bmatrix}0 & 1 \\ 1 & 0\end{bmatrix}, \sigma_y = \begin{bmatrix}0 & -i \\ i & 0\end{bmatrix}, \sigma_z = \begin{bmatrix}1 & ...
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What are the main obstacles to overcome to build silicon-photonic quantum computers?
In superconducting quantum computers, we use mostly superconducting qubits or trapped ions. However, those systems are quite large because their environment either requires near absolute zero ...
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What are the ranges of the four $q$ parameters in the magic simplex of Bell states formula?
Equation (7) in the 2012 paper, "Complementarity Reveals Bound Entanglement of Two Twisted Photons" of B. C. Hiesmayr and W. Löffler for a state $\rho_d$ in the "magic simplex" of Bell states
\begin{...
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How does quantum memory work using atoms?
I was trying to learn quantum memory and went through some papers, websites, etc.
The current understanding I have (which I'm not sure is right) is this: Two photons are prepared together which are ...
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How to explain polarization using photon spin?
I know how polarization filters work using EM waves. Can somebody help me in understanding how they work using photons?
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Implementing BB84 protocol with easily-obtained consumer hardware
Following on from my question on educational quantum computing toys, I was wondering whether it is possible to implement the BB84 key distribution protocol with easily-obtained consumer hardware - ...
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