Questions tagged [physical-qubit]

For questions related to physical realizations of quantum bits i.e. quantum systems living in a 2-dimensional Hilbert space.

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Is it possible to perform quantum computation between different Hilbert spaces?

Let us consider a protocol between Alice and Bob. Alice works in a $2^n$-dimensional Hilbert space $\mathcal{H}_A$, using $n$ qubits. Bob works in a $(1+2^n)$-dimensional Hilbert space using qdits. ...
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1answer
28 views

What does a gate electrode do in the context of a quantum dot?

I am trying to understand the creation of qubits through the use of quantum dots, but I have always had some trouble understanding the function of the gate electrode. I know it can control the ...
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What is a qubit's impulse response?

As far as I know, qubits are primarily measured in the frequency domain, sending a relatively long, spectrually pure pulse to interrogate the qubit's state. In general, what would happen if you sent a ...
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On the IBM-Q experience, how do different frequencies for different qubits affect results?

I've been looking at the graphs of various Quantum Processors on IBM-Q experience and for qubits, frequency of different qubits is the first statistic shown. From this in the Qiskit textbook: The ...
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1answer
119 views

How significant is achieving electronic transport in a single qubit at room temperature?

This is a follow-up to a previous question I asked: How promising is the possibility of carbon-based qubits to make a qubit that’s stable at room temperature? I am trying to assess the significance of ...
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1answer
43 views

What is the difference between SWAP & Bridge gates?

While I'm studying about Qubit allocation (mapping), I wonder what the differences between SWAP and Bridge gates are. I know that a SWAP gate and Bridge gate can be represented with 3 CNOT gates and 4 ...
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512 views

Non-layperson explanation of why a qubit is more useful than a bit?

I have a computer science and mathematics degree and am trying to wrap my head around quantum computing and it just doesn't seem to make sense from the very beginning. I think the problem is the ...
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1answer
111 views

What design considerations set the frequency bounds for superconducting qubits?

Superconducting qubits generally have frequencies within the range of 4 - 8 GHz. What design considerations give the upper and lower bounds for what is a feasible design. I.e, why can't they be higher ...
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292 views

What's the default value for a quantum register?

I've just started to learn Quantum computing with Qiskit: I'm reading the Qiskit documentation and the book "Quantum Computing in Practice with Qiskit® and IBM Quantum Experience®". In this ...
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956 views

How can one imagine entanglement in a non-mathematical way?

I understand the theoretical concept of an entanglement and what it means for our computation to have two entangled qubits, but what does it really mean when two qubits are entangled? How are they ...
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1answer
69 views

What is the meaning of measuring a Bell state with Pauli operators?

There will be a certain value of getting the probability when measuring any Bell's state with Pauli operators such as observable X, Y, or Z. What is the meaning behind all this measurement? the result ...
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2answers
78 views

How instantaneous is state preparation in a quantum register, if all possible superpositions are to be initialized equally?

Before the start of a quantum algorithm qubits need to be initialized into a quantum register. How fast can a quantum register of length $n$ be initialized in a way that all possible superpositions of ...
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123 views

What is the problem in demonstrating quantum supremacy?

I am new to the quantum world and it's computing. But it accidentally hit in my mind that DWave built a quantum computer with 2000 qubits which can be use to simulate the whole observable universe or ...
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471 views

Qubit Connectivity of IBM Quantum Computer

When simulating a quantum circuit using qiskit qasm_simulator, the qubits that you assigned to the quantum circuit can be ...
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2answers
290 views

What exactly does it mean to embed classical data into a quantum state?

As the title states. I am a Machine Learning Engineer with a background in physics & engineering (post-secondary degrees). I am reading the Tensorflow Quantum paper. They say the following within ...
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1answer
32 views

What are some resources on qubits based on quantum dots?

I would like to learn a bit on the physics and details of manufacture of a qubits based on quantum dots. Can anyone recommend some papers?
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What are the pros/cons of Trapped Ion Qubits, Superconducting Qubits and Si Spin Qubits?

Among available qubit technologies for universal quantum computing these 3 come up as promising. NV centers and Majorana qubits also underway but relatively new. I find superconducting qubits and ...
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1answer
74 views

How do quantum gates work on qubits in the physical world?

How do quantum gates work on qubits in the physical world? What are different ways through which qubits can be manipulated in the physical world? For example, by analogy a classical NOT gate uses ...
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1answer
66 views

In $|x_1,…,x_n\rangle$, can the individual constituents be called qubits?

A qubit is a quantum system in which the Boolean states 0 and 1 are rep- resented by a prescribed pair of normalised and mutually orthogonal quantum states labeled as ${|0⟩, |1⟩}$ According to [1]. ...
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1answer
49 views

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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1answer
40 views

What determines the topology/connectedness of quantum computers?

Some quantum computers hold their qubits in a 2D array. I've even seen a 1D topology I think. On IBM Q, you can see which qubits talk to which qubit. I would like to know what determines/limits the ...
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54 views

How do you CNOT between qubits faraway from each other?

I'm just curious. Say I have 3 qubits on a straight line 0-1-2. How do you guys (on the IBMQ or Rigetti team for example, or anyone who actually works on quantum computer) entangle 0-2 if I, say, am ...
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1answer
64 views

How promising is the possibility of carbon-based qubits to make a qubit that’s stable at room temperature?

Here is the first article I could find on this idea in 2016: https://arxiv.org/abs/1611.07690 And here is a patent in 2017 for a quantum electronic device developed with one of the authors of the ...
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50 views

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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294 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). ...
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1answer
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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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56 views

Calculating the state of the qubit when $\alpha$ and $\beta$ are given [closed]

I am new to quantum computing. Can someone help me in calculating state of the qubit when $\alpha = \frac{3}{5}e^{i\pi/7}$ and $\beta = -\frac{4i}{5}$. Thanks
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252 views

Is there anything practical that can be done with a single qubit?

Is there anything practical that can be done with a single qubit? And by "practical," I mean a problem that can be solved or information that can be stored. I realize that one practical thing that ...
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1answer
85 views

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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48 views

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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102 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 ...
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1answer
75 views

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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81 views

How do I explain qubits to my cousin who is 8 year old?

How do I explain qubits to my cousin who is 8 years old?
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How do physical implementations of Z gate selectively affect $\lvert1\rangle $ basis vector?

The Pauli Z gate inverts the phase of $\lvert1\rangle $ while leaving $\lvert0\rangle$ unaffected. When I think about how $\lvert1\rangle $ and $\lvert0\rangle$ are physically realized, however, as ...
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149 views

Atom magnetic moment caused by orbiting electron

In Nielsen and Chuang Quantum Computation and Quantum Information book section 1.5.1 describing the Stern-Garlach experiment, it says: "Hydrogen atoms contain a proton and an orbiting electron. You ...
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329 views

Can a classical limit of qubit emerge on a classical computer? [closed]

Hello, I am uncertain; however, today at a toy museum, I might have captured a qubit on a classical computing structure, “ a broken 90-marble abacus,” as shown in the attached photos above. I did ...
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2answers
880 views

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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1answer
343 views

Why are superconducting qubits the most popular approach to build a quantum computer?

There are many different physical implementations of qubits: NMR, spin qubit, N color center in diamond, superconducting qubit, trapped ions, photonics quantum computing, topological qubit, etc. ...
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Is quantum superposition state a truth or an assumption?

Please, be patient with my question I already read that there is a heuristic that makes superposition a fact of reality. In addition, this superposition, when observed, it has a state of 0 or 1. ...
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6k views

What does it mean for two qubits to be entangled?

I have done some sort of online research on qubits and the factors making them infamous i.e allowing qubits to hold 1 and 0 at the same time and another is that qubits can be entangled somehow so that ...
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1answer
102 views

What is the difference between superposition of $|0\rangle$ and superposition of $|1\rangle$ at physical level?

If we apply Hadamard gate 2 times on a qubit $|0\rangle$ then we will get $|0\rangle$. So there must be something else which is unique for both $|1\rangle$ and $|0\rangle$ which is constant even in ...
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1answer
113 views

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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474 views

Why do the IBM and Google processors both have 53 qubits?

As I understand from this IBM post both the IBM and Google teams have independently built 53-qubit processors. What is the significance of the number 53? It is purely coincidental, or is there a ...
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160 views

Converting a qubit's state to a binary value in Q#

In Q#, How do I store a qubits state in a binary-based disk / hard drive for use by regular digital programs? Is this even possible?
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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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181 views

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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38 views

Excitation of a superconducting circuit

What do we mean by exciting a superconducting circuit--which represent a qubit, how they are get excited inside? how the two states of the qubit are represented in this circuit?
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1answer
33 views

Measuring a quantum wire at t > 0

I saw on the site Brilliant.org a question witch is: "Let's say I'm given a quantum wire, I measure it and find it charged "on". If I come back some time later, what state should I measure?" And the ...
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3k views

What is the difference between transmon and Xmon qubits?

Transmon and Xmon qubits are two types of superconducting charge qubits that seem to be often used in superconducting quantum devices. However, I wasn't able to easily find direct comparisons between ...
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Charge Qubit vs Transmon

I want to know the big difference, in terms of fabrication (circuit) between a charge Qubit and a Transmon, how is a Transmon less affected by noise ? Many thanks