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Questions tagged [optical-quantum-computing]

For questions about the specific realization of quantum computing that uses photons as qubits. Examples of gates include the Fabry-Perot cavity or linear optical components like beamsplitters. Questions with this tag can ask about both theory and practice, as long as it relates to this specific realization.

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Can we apply only the annihilation operator on Strawberry Fields?

Strawberry Fields allows us to access photonic hardware for continuous variable quantum computing. I was wondering if we can implement just the $\hat{a}$ (annihilation operator) on coherent state $|\...
Chetan Waghela's user avatar
1 vote
1 answer
177 views

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.
physics22's user avatar
2 votes
0 answers
83 views

Quantum Process Tomography for 2 qubits

I need clarification on a few aspects related to Box 8.5 and Exercise 8.34 from the book Quantum Computation and Quantum Information by Nielsen & Chuang . While attempting Exercise 8.34, I ...
Sachindra Kumar's user avatar
1 vote
0 answers
68 views

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 ...
Ryan Wang's user avatar
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2 votes
2 answers
132 views

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
3 votes
1 answer
220 views

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
  • 491
1 vote
1 answer
169 views

I was solving matrix of beam splitter in python but got stuck in understanding the library

What does this command physically mean? block_diag([[1]], BSunitaries[2], [[1]]) Can any one tell me in matrix form? Source
owais ishtiaq's user avatar
0 votes
1 answer
103 views

Diagonal elements of the transition dipole moment

I'm currently doing some work in Quantum Optics and now have a question about the transition dipole moment. We were told in class that the off-diagonal elements of this matrix, namely $\langle n|d|m\...
SphericalApproximator's user avatar
2 votes
0 answers
285 views

Measurement Base of Fusion Gate

I am reading this article on "Fusion-based quantum computation" and they claim there about Fusion Gate type-2 that it collapses the state to 2 types of eigenstates, and returns 2 results - $...
Ron Cohen's user avatar
  • 1,402
3 votes
2 answers
824 views

Modular exponentiation quantum circuit design for Shor's algorithm

I'm studying Shor's algorithm and I'm wondering how to build the quantum circuit for the modular exponentiation calculation in the Shor's algorithm. Is the circuit found classically (using ...
William's user avatar
  • 162
1 vote
0 answers
136 views

qutip.sesolve and qutip.optimize_pulse_unitary produce different results

I'm currently trying out some things with qutip in the field of optimal control (state-to-state transfer) and have some trouble to reproduce my results from the optimization process with sesolve. My ...
SphericalApproximator's user avatar
-2 votes
1 answer
143 views

Does this quantum algorithm to check for a permuting function make sense? [closed]

Even "Deutsch's algorithm" seems too difficult. Maybe I found an algorithm that is more appropriate for people without knowledge. Less to explain. Easy to understand. Or do you have ...
Marco Schmid's user avatar
1 vote
1 answer
421 views

QuTIP tensor products

I am referring to the QuTIP package https://qutip.org/ To describe a system of 3 atoms in the ground state, I can crate the wavefunction: tensor( basis(2,0), basis(2,0), basis(2,0) ) Now suppose that ...
Halo's user avatar
  • 13
3 votes
0 answers
46 views

How to quantify trace distance between two matrices representing two quantum optical networks?

This is my first post here, so I'm sorry if this question could be ill-formulated. I have performed measurements on a 12x12 optical quantum network, so that I have a stochastic matrix $P^{exp}$ where ...
v_enushk's user avatar
6 votes
1 answer
576 views

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
  • 365
0 votes
1 answer
110 views

Knill Laflamme conditon

In Preskill's notes on quantum error correcting codes in Section 7.2, there seems to be no condition on the environment part of the state, i.e. $|0\rangle_E$ in $|\psi\rangle \otimes |0\rangle_E$. ...
alpha's user avatar
  • 109
3 votes
1 answer
271 views

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 ...
Blue Herring's user avatar
2 votes
1 answer
147 views

How to solve non-"cross-damping off" Linblad equation in QuTiP?

As I understand from the official QuTiP guidlines, it is only capable of solving "cross-damping off" Master Equation in form: $\dot{\rho(t)} = -\dfrac{i}{\hbar}[H(t),\rho(t)] + \sum\limits_n\...
mesolver's user avatar
4 votes
0 answers
111 views

Why is it important to perform optical quantum computing with ONLY linear components?

The main achievement of the KLM protocol is demonstrating that quantum computing can be done with only linear optical elements, i.e., beam splitters, phase shifters, single-photon sources, and photo-...
LearnerAL's user avatar
1 vote
1 answer
1k views

What are the pros and cons of the most popular QC architectures?

I notice numerous companies and research groups around the world trying to build QC's with wildly different approaches. Intuitively, this suggests to me that QC is still very early in its maturation - ...
Andrew's user avatar
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2 votes
1 answer
216 views

Comparing technical limitations of major quantum computing approaches

As far as I know, major quantum computing approaches include superconducting qubits, trapped ions, nuclear magnetic resonance qubits, and free space quantum optics. I guess two main technical ...
LearnerAL's user avatar
0 votes
1 answer
42 views

Can such a transformation be implemented by using just polarizers?

Consider a transformation $U_a=\sigma_z^{a_1}\otimes...\sigma_z^{a_N}$, here $\sigma_z$ is the Pauli Z operator. $a_i$ is either 0 or 1. Hence, $\sigma_z^{0}=I$ where $I$ is identity matrix. If I use ...
Chetan Waghela's user avatar
4 votes
0 answers
49 views

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
0 answers
33 views

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
3 votes
1 answer
119 views

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
5 votes
0 answers
128 views

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
  • 51
6 votes
2 answers
471 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
89 views

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
  • 437
5 votes
2 answers
349 views

What is the correct sign in the unitary evolution operator of a beam splitter?

I'm a bit confused about which is the correct sign in the unitary evolution operator of a beam splitter. In paper Digital quantum simulation of linear and nonlinear optical elements author uses the ...
Dani's user avatar
  • 267
3 votes
0 answers
209 views

Timing accuracy for the KLM protocol and how do controlled gates work?

I'm working on an open-source and open-hardware implementation of the KLM protocol, currently I'm working on EDA software that converts OpenQASM code into a manufacturable PCB As part of that, I need ...
Noah Wood's user avatar
4 votes
0 answers
88 views

Boson Sampling with a single beamsplitter

In Boson Sampling as first proposed by Aaronson and Arkhipov in arxiv.org/abs/1011.3245, the interferometer is made up of phase shifters and beamsplitters. As these gates are universal, drawing the ...
Marsl's user avatar
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6 votes
1 answer
228 views

Shor's Code: Understanding how it satisfies Knill Laflamme Theorem

I'm new to Quantum Error Correction, and I have a question on Shor's Code. If we have a protected subspace, $V \subset \mathbf{C}^2\otimes \cdots \otimes \mathbf{C}^2$ $V=\operatorname{span}\{|0_{...
Anon's user avatar
  • 161
2 votes
1 answer
525 views

Hamiltonian for Single-photon, Single-atom QED Cavity

Equation 7.71 of Nielsen and Chuang's Quantum Computation and Quantum Information gives the Hamiltonian for a two level atom and single mode photons in a cavity as: $H = \hbarωN + δZ + g(a^†σ_− + aσ_+...
Bashir's user avatar
  • 159
3 votes
0 answers
43 views

How to perform quantum logic gates on plasmons?

In the link provided researches utilize strong two-plasmon absorption in graphene nanoribbons to create a “square-root-of-swap”, could such a device be utilized to perform other quantum logic gates? ...
Marko Miloradovic's user avatar
6 votes
1 answer
595 views

Physical qubit of optical quantum computer

I was researching how optical quantum computers work and discovered a KLM protocol that allows for building quantum gates using linear optics elements like mirrors, beam splitters, and phase shifters. ...
Aleksandar Kostovic's user avatar
8 votes
0 answers
283 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
5 votes
2 answers
189 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
20 votes
1 answer
615 views

Is "probabilitistic,universal, fault tolerant quantum computation" possible with continuous values?

It seems to be a widely held belief within the scientific community that it is possible to do "universal, fault-tolerant" quantum computation using optical means by following what is called "linear ...
rrtucci's user avatar
  • 679
20 votes
3 answers
1k views

Is it possible to "calculate" the absolute value of a permanent using Boson Sampling?

In boson sampling, if we start with 1 photon in each of the first $M$ modes of an interferometer, the probability of detecting 1 photon in each output mode is: $|\textrm{Perm}(A)|^2$, where the ...
user1271772 No more free time's user avatar
10 votes
1 answer
262 views

What is the status of quantum computing compared with other (photonic) quantum technologies?

There is a number of emerging quantum technologies, among which we find the category of photon-based quantum technologies, including quantum key distribution or quantum random number generators. The ...
agaitaarino's user avatar
  • 3,827
10 votes
1 answer
732 views

How do you apply a CNOT on polarization qubits?

I read that a qubit can be encoded in a polarization state (horizontal or vertical polarization of a photon). How do you perform two-qubit operations on a polarization qubit?
Daniel Tordera's user avatar
6 votes
1 answer
727 views

What is the relation between single photon qubits and squeezed light qubits?

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 ...
Daniel Tordera's user avatar
7 votes
2 answers
465 views

Improving probability of spontaneous parametric down conversion

As mentioned in an earlier question of mine, I am interested in using type one spontaneous down conversion (SPDC) in optical quantum computing. However, SPDC is a somewhat low probability occurrence - ...
auden's user avatar
  • 3,459
25 votes
3 answers
3k views

Why do optical quantum computers not have to be kept near absolute zero while superconducting quantum computers do?

This is a follow-up question to @heather's answer to the question : Why must quantum computers be kept near absolute zero? What I know: Superconducting quantum computing: It is an implementation of ...
Sanchayan Dutta's user avatar
11 votes
2 answers
1k views

State produced by spontaneous parametric down-conversion (SPDC)

I'm researching SPDC's efficacy for use in an optical quantum computing model and I've been trying to figure out exactly what state the photons are in when they come out (as represented by a vector, ...
auden's user avatar
  • 3,459