Questions tagged [physical-realization]

For questions about practical computers or processors that run on a quantum architecture. This is for questions about the machines themselves, not just any computing that could take place on one. You may also use this tag for questions on realistic implementations of quantum channels. DO NOT use for questions about simulation or emulation of quantum computers, or cloud-based quantum computing services like the IBM Q Experience.

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What are some general concepts of how a classical computer would interface with a quantum computer?

Very general question so I'm not looking for an exact answer. I just want a basic description of certain ways it can be done and then if possible the names of those ways, so that I can look them up ...
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How to implement a while loop?

How can a while loop be implemented in a quantum computer? If quantum computing consists of : preparing a state applying a unitary operator measuring, then it seems like it's not possible to wait ...
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What are the practical limitations of complementing quantum computations with memristors?

Considering the current state of research into quantum memristors, and the advantages/disadvantages of quantum and memristor driven computing architectures: Quantum Memristors Quantum Memristor ...
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Can we have multiple-state unit for quantum computer?

All quantum computers now are working with qubit which is zero or one. Can we have quantum computer with multiple-state unit? Such as trit (trinary, 3 states), digit (10 states) instead of qubit (2 ...
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Do all physical architectures for quantum computers use the same universal gate sets?

Now I have understood that physical implementation of quantum computer need a universal quantum gate set like Clifford+T to realize any unitary quantum gate. However, I don't know if it is all the ...
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Is it possible to create a quantum computer with a double-slit or Stern-Gerlach apparatus?

If we choose double-slit, can we put multiple "slits" and create calculation for just one algorithm (problem, solution...)? Not general purpose quantum CPU, just for one. Same question for Stern-...
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Software used for modelling quantum processors

What kind of software is used for modelling quantum processor architectures? Not just simulate the output, but the one that is actually used in research.
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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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Moore's law for quantum computers

Moore's law states that performance of classical computers doubles every two years (later revised to 18 months) and a price for computing resources halves during same time period. Currently, it seems ...
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Is there any legitimate information about Microsoft quantum hardware?

I'm wondering if anyone has information regarding the current status of Microsoft quantum hardware? How many working qubits do they have? What are the gate depth/fidelity? Any details about ...
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1answer
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Exponential Growth of Noise in Quantum Computers

I recently listened to a presentation for Introductory Quantum Computing. It was very general and meant to give the listeners an idea about the potential for Quantum Computing. The speaker ended the ...
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Is it possible to build a quantum processor with connections among all qubits?

Current quantum processors have constrained connectivity among qubits. For example Starmon-5 processor by Quantum Inspire has only one qubit connected to others, effectively it looks like a star. The ...
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Long range two qubit gates in superconducting qubits

In superconducting qubits, all the method that I have seen until now are based on short range interaction. For example you have two qubits to process information around a middle qubit that is ...
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What are examples of quantum computing platforms availble for free (other than IBM Q)?

IBM Q is (maybe first) quantum computing platform allowing users to register for free and run algorithm on real quantum processors. There are several processors with usually 5 qubits, however, it is ...
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On the complexity of an oracle for a classical function

Let us assume that we have a classical function $f:\{0\,;\,1\}^n\to\{0\,;\,1\}^m$ which is efficiently computable. Then, its oracle is defined with $\mathbf{U}_f\,|x\rangle\,|y\rangle=|x\rangle\,|y\...
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How qubit phase is build in real hardware?

How qubit phase is build in real hardware? On IBM Quantum, D-Wave, etc?
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$H = e^{i\pi/4} \sqrt{iNOT}$?

In the paper Valley qubit in Gated MoS$_2$ monolayer quantum dot, a description of how a $NOT$ gate would be performed on a qubit in the described device is given. The authors say that in the ...
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Topological quantum computer and two dimensional materials

Recently I read thread on topological quantum computers. If I understood correctly, gates in such computers are based on "effects" in two dimensional spaces. Since our space is three dimensional, such ...
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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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Readout using an NMR spectrum

I'm trying to understand how to read results from an NMR quantum computer. According to Nielsen and Chuang: The principal output is the free induction decay signal $$V(t) = V_0\text{Tr}\left[e^{-...
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Why does non-locality and the particle-hole symmetry not contradict each other?

Currently, I'm learning about topological quantum computers. In one of the explained techniques, cooper pairs in superconductors are considered, where a cooper pair with a hole form a Majorana bound ...
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Physical implementation of gates on IBM Q

There is a lot of quantum gates in IBM Q Composer, however, only few are implemented physically while others can be composed of them. When one looks at description of a quantum processor in IBM Q ...
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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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How to deal with the relative phase from the evaluation of the not interacting qubit?

Every qubit is a realization of some two-level quantum system with $\left| 0 \right\rangle$ and $\left| 1 \right\rangle$ states. These states have their energies $E_0$ and $E_1$ respectively. By ...
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Which subatomic particle does each company use in quantum computing?

Probably each company (Google, Amazon, Intel, IBM, Microsoft, D-Wave and so on) uses a mix of subatomic particles and technologies. I would like to know which particles/technologies are used by each ...
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The Clock Speed for the Quantum Computers

Is there a way to look up the clock speed for the different computers?
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How will quantum computers access large amounts of storage?

I've seen many articles in the popular press saying that quantum computers will enable searching through huge amounts of data in an instant. But I can't figure out how the current architectures can do ...
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Where are the physical gates in the Google processor?

Google's article Quantum supremacy using a programmable superconducting processor states that the processor "53 qubits, 1,113 single-qubit gates, 430 two-qubit gates, and a measurement on each qubit, ...
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Building a DIY quantum computer - how to reduce a noise?

I refer to A DIY Guide to Building a Quantum Computer and Researchers advance noise cancelling for quantum computers. With my friends, I would like to build our simplified quantum computer. We are ...
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What is the state of the art on Quantum Random Access Memories? [duplicate]

I realized that Quantum Random Access Memory (qRAM) was proposed to make quantum computers more similar to classical one. Currently quantum computers have very constrained memory, given only quantum ...
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How are states of a qubit measured in a quantum computer? [closed]

How is a state of a qubit measured physically on a quantum computer?
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What are the general hardware components of a universal quantum gate computer?

Although the architecture of a quantum computer depends on the implemented qubit system, I still wonder what the general structure of hardware parts would be. Evidently, a quantum computer isn't ...
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How is a quantum computer programmed?

After lightly reading into quantum algorithms and the hardware of quantum computers, I subsequently started wondering how a quantum computer is programmed so it executes the desired quantum algorithm ...
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Why are multiple quantum gates, in a quantum circuit, used?

After reading about quantum computers, for a high school research paper, a few questions arose concerning quantum logic gates. At first, it seems that quantum logic gates are in essence various ...
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How many types of quantum computers are currently being researched? [duplicate]

I came across a "new" type of quantum computer - photonic quantum computing. Is this type of technology of interest here? You may read about an example here. I wonder how many types of quantum ...
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Color-Space as Effective and Intuitive Qutrit Physical Realization? [closed]

Has anyone used or considered color-space and color superposition for Qutrit work? A classical color-sphere has black and white at its poles, a grey scale as its axis, pure spectral colors as a color-...
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What are the physical reasons behind noise/errors in quantum computers?

We know that the current quantum computers are noisy/error-prone. They are susceptible to gate errors (single qubit and multi-qubit), decoherence (relaxation and dephasing), readout error, etc. I want ...
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Why use U2 and U1 gate in IBM quantum computers?

I was wondering why IBM's computer were using U1 and U2 gates as part of there basis gates since as I understood, they are particular cases of the U3 gate. Why not just use U3 gate instead ? Thanks ...
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Why don't qubits continuously rotate in the $z$ direction due to free time evolution?

If we have a physical qubit with energy eigenstates $|0\rangle$ and $|1\rangle$ with energy separation $\Delta E$ its Hamiltonian in the absence of any interaction is $$H=\hbar\frac{\Delta E}{2}\...
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What is the difference between a cooper pair box and a transmon qubit?

These two kinds of qubits are both classified under "charge qubits", looking for them, I always find the same circuit representation. Occasionally, I find one where there's a SQUID instead of the ...
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Looking for papers that are pessimistic about the feasibility of a quantum computer

I'm actually searching two types of documents (could be the same): 1) A synthesis about all the main gap/problems that make the physical realisation of a quantum computer actually infeasible. 2) ...
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quantum circuit with feasible gates for state preparation

I have a classical vector of size $2^{n}$ (normalized) and I want to use this value as amplitude for my $n$ qbits, in the canonical basis $|00000\rangle$, $|00001\rangle$ etc. I want to use real ...
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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? ...
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Physical realization of qubits with superconducting Josephson junctions

Does anybody know how to explain briefly how to realize qubits (initialization, states transition, measurements,..) with superconducting Josephson junctions, say DC-SQUIDS?
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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. ...
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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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How is a physical qubit measured and how is the result interpreted?

To my understanding, most of the qubits we use today are just Josephson junctions coupled to a resonator that is triggering the qubits to go to different states by using microwave pulses. The same ...
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How are witness operators physically implemented?

Let's take an example of an entanglement witness of the form $W = | \phi \rangle \langle \phi | ^{T_2}$ where $ | \phi \rangle $ is some pure entangled state. If I wanted to test some state $\rho$, I ...
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IBM's quantum computing capabilities — entangled 18-qubit GHZ states and high coherence times

Here's a blog post that corresponds with what IBM presented at the 2019 March Meeting. In this post, they claim they've measured qubit T1 relaxation times above 500 microseconds, and claim that they'...
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What quantum volume is needed to represent a single logical qubit?

The quantum volume metric $V_Q$ is a proposed metric for quantifying and comparing the performance of quantum computers1. The quantum volume is defined as $$V_Q = \max_{n<N} \left(\min\left[n, d(n)...