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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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 ...
Alexey Uvarov's user avatar
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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- \...
Michael.Andy's user avatar
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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 ...
Michael.Andy's user avatar
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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 ...
symmetry-question-haver's user avatar
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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 ...
Daniele Cuomo's user avatar
3 votes
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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....
user111's user avatar
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What is the next milestone in quantum computing?

I have heard it mentioned that the first milestone for quantum computing is any sample implementation of quantum advantage. As we are presumably already there now (with boson sampling), the next ...
James's user avatar
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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-...
James's user avatar
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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 ...
Onur-Andros Ozbek's user avatar
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Encoded Fusion Based Ring Resource State

In the article on Fusion Based Quantum Computing, they presented that a fusion of 4qubits encoded states, is creating an encoded ring resource state. My question is - when we make fusion (Type 2) to 2 ...
Ron Cohen's user avatar
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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 (...
유승연's user avatar
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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?...
MementoMori's user avatar
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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 ...
mehrosadat ebrahimi's user avatar
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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....
Daniele Cuomo's user avatar
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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 $\...
Daniele Cuomo's user avatar
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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 ...
Natchapol Patamawisut's user avatar
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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 ...
Marion's user avatar
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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 = ...
tparker's user avatar
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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 ...
david's user avatar
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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 ...
Tyler Selden's user avatar
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1 answer
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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 ...
Fateh's user avatar
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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 ...
Mimo Pakou's user avatar
2 votes
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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?
Mimo Pakou's user avatar
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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 ...
Mimo Pakou's user avatar
6 votes
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253 views

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, ...
alexhak's user avatar
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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 ...
quest's user avatar
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7 votes
1 answer
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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 ...
ile2N's user avatar
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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 ...
Spock's user avatar
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1 answer
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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 ...
Dunbar Birnie's user avatar
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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). ...
Pranav Jain's user avatar
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1 answer
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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 ...
Devjyoti Tripathy's user avatar
3 votes
2 answers
592 views

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). ...
Pranav Jain's user avatar
3 votes
1 answer
496 views

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 ...
yousef elbrolosy's user avatar
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0 answers
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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 ...
user820789's user avatar
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2 votes
1 answer
340 views

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 ...
user820789's user avatar
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3 votes
1 answer
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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 ...
user820789's user avatar
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5 votes
2 answers
352 views

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 ...
Jack Ceroni's user avatar
5 votes
0 answers
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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 ...
Sam's user avatar
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1 answer
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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 ...
zircon's user avatar
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5 votes
2 answers
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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 & ...
QuestionEverything's user avatar
8 votes
0 answers
241 views

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 ...
Aleksandar Kostovic's user avatar
3 votes
1 answer
83 views

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{...
Paul B. Slater's user avatar
4 votes
1 answer
256 views

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 ...
Swaroop Joshi's user avatar
1 vote
1 answer
196 views

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?
Tech Solver's user avatar
1 vote
1 answer
123 views

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 - ...
ahelwer's user avatar
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3 votes
2 answers
139 views

Phase shifter acting on double rail states

In Nielsen and Chuang, it is stated that the photonic phase shift gate acts on the single photon states as $P|0\rangle \ = \ |0\rangle$ and $P|1\rangle \ = \ e^{i\Delta}|1\rangle$, where $\Delta \ = \ ...
Jack Ceroni's user avatar
5 votes
2 answers
170 views

Multi-photon states in photonic quantum computing?

Within photonic quantum computing, one of the ways to represent information is the dual-rail representation of single-photon states ($c_0|01\rangle \ + \ c_1|10\rangle$). Is it possible to utilize ...
Jack Ceroni's user avatar
4 votes
2 answers
234 views

Time-bin encoding qudits

Time-bin encoding is a technique used in Quantum information science to encode a qubit of information on a photon. Wikipedia Is there a generalization for $n$-th level qudits?
user820789's user avatar
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3 votes
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Photonic CHSH Games

How can a CHSH game be realized in a photonic circuit?
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