2022 Developer Survey is open! Take survey.

Questions tagged [superconducting-quantum-computing]

For questions about the superconducting realization of quantum computers. Questions can be about both the implementation of this realization or the theory behind this realization. If you are asking about a specific aspect of superconducting quantum computers, please also tag with that (i.e., if you are also asking about the Josephson junction, tag with that).

Filter by
Sorted by
Tagged with
0 votes
1 answer
17 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\...
user avatar
  • 21
3 votes
1 answer
184 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 ...
user avatar
  • 55
2 votes
1 answer
55 views

Good review articles on microwave hardware for superconducting qubit quantum computing?

I am trying to find some review articles on the microwave hardware used in superconducting qubit quantum computing. So far, most papers that I found seem to be high level overviews, e.g., Multilayer ...
user avatar
2 votes
0 answers
23 views

What is the dipole moment of a typical transmon qubit?

What is the dipole moment of a typical transmon qubit? I know this depends on the specific size, and that that varies from design to design. So let me provide an example situation: So given this size ...
user avatar
  • 1,230
-2 votes
1 answer
130 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 ...
user avatar
-2 votes
1 answer
82 views

Simultaneous computational basis measurement

Many quantum algorithms requires measurements at the end of the processing and it seems like the quantum state measurement setup is required to be made for measuring the two computational basis. I ...
user avatar
  • 55
2 votes
0 answers
48 views

Individual processing of quantum circuit measurment results

When superconducting transmon qubits are measured with a readout pulse, the raw readout signal is demodulated, and results appear as clouds on the IQ plane, with one point in the cloud representing ...
user avatar
  • 1,230
2 votes
0 answers
51 views

What does the $\sigma_z$ operator correspond to in the context of a Transmon qubit?

In the context of the transmon qubit and an LC circuit with a coupling capacitor and driving voltage. We can write the charge operator $Q$ as $-iQ_{ZPF}\sigma_y$ (since we defined $Q$ using the ladder ...
user avatar
4 votes
0 answers
35 views

Meaning of Continuous Charge in the Inductively Shunted Cooper Pair Box [closed]

In the Cooper Pair box, the conjugate momentum $\hat{n}$ of the reduced superconducting phase variable $\hat{\varphi}$ takes only discrete, integer values due to the $2\pi$ periodicity of the phase. ...
user avatar
7 votes
1 answer
338 views

Is the Solovay-Kitaev theorem relevant for modern hardware?

The Solovay-Kitaev theorem (and more recent improvements) explains how to efficiently compile any 2-qubit unitary into any universal (dense) finite set of gates. My question is if this theorem is ...
user avatar
5 votes
1 answer
64 views

How do we know that a superconducting circuit is a quantum system?

In introductions to superconducting qubits, we often take the classical LC circuit and then quantize the operators. Why are we allowed to do this? I do not see this derivation anywhere -- what ...
user avatar
3 votes
1 answer
68 views

How are gates implemented in a transmon qubit?

A transmon qubit is fundamentally in LC circuit. How are gates implemented in a transmon qubit? How do we know what voltage corresponds to the $\sigma_x$ gate for example?
user avatar
5 votes
1 answer
110 views

In a transmon qubit, what corresponds to the ground and excited states?

In a transmon qubit, we have ground and energy eigenstates but what is actually happening in the circuit here? How do the current and voltage look? It looks like its made up of things you would find ...
user avatar
4 votes
1 answer
80 views

What does it mean to be in a superposition of eigenstates in a LC oscillator?

In superconducting qubits, we use a circuit with a specific type of inductor and quantize the Hamiltonian. Because it's an anharmonic oscillator, we say that it has states -- $|0\rangle$ and $|1\...
user avatar
1 vote
0 answers
34 views

Are there differences in how quantum error correcting codes are applied on superconducting vs. trapped ion systems?

Are there any differences in how quantum error correcting codes are currently applied on superconducting vs. trapped ion systems?
user avatar
1 vote
0 answers
25 views

What is the role of Josephson junctions and biases in the D-Wave qubit structure?

On the D-Wave 2000Q there are up to 2048 qubits and 5600 coupler. A commonly used picture of one of such qubits is attached below. Each qubit is realized by a loop of niobium controlled by Josephson ...
user avatar
  • 11
3 votes
0 answers
55 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-...
user avatar
1 vote
1 answer
92 views

Can we actually do quantum teleportation in IBM quantum computers?

I am going through a course in Quantum computation by NPTEL-IBM, which is designed to introduce Qiskit. In one lecture they describe the concept of quantum teleportation, and point out that since IBMQ ...
user avatar
  • 203
3 votes
0 answers
52 views

How to design a RF-SQUID qubit by Qiskit Metal?

I am now learning how to use Qiskit Metal to design superconducting circuits. I found that there are only several transmon qubits in the library. Can I design an RF-SQUID qubit by using Qiskit metal? ...
user avatar
2 votes
2 answers
104 views

Are composite gates within superconducting hardware implemented as a single pulse or as a series of pulses?

If we have for example a gate $U^{\otimes2}$, then within superconducting hardware, is the $U$ applied onto the first qubit and then the second or is a pulse corresponding to a composite gate (tensor ...
user avatar
  • 139
-1 votes
1 answer
236 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 - ...
user avatar
  • 101
2 votes
1 answer
72 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 ...
user avatar
9 votes
1 answer
59 views

Is there an intuitive way to conceptualize the ground and excited states of a transmon qubit?

I understand how a transmon qubit is analogous to an LC circuit, but has an anharmonic energy spectrum due to the nonlinearity of the Josephson junction. I also understand how to write out the ...
user avatar
2 votes
1 answer
84 views

How does the pulse.Shiftphase instruction in Qiskit Pulse work? [closed]

I have some questions regarding the mechanism of Qiskit pulse.ShiftPhase instruction: Does it work like a Phase Shift $P(\theta)=\begin{bmatrix} 1 & 0 \\0 &...
user avatar
5 votes
1 answer
96 views

How do the extra energy levels of a transmon qubit affect computation/fidelity?

I was reading about transmon qubits, and I know that they are not true two-level systems. Are there any math/papers which talk about how those extra energy levels affect the computation? I'm assuming ...
user avatar
  • 81
4 votes
1 answer
453 views

What is the IQ plane?

I struggle to find any information on Nielsen and Chuang or similar texts on the exact definition of the so-called IQ plane (I think this is a notion closely related to solid state quantum computers ...
user avatar
  • 419
3 votes
0 answers
34 views

Clean way of approximating an oscillator by a qubit

Let me consider a (quantum) Harmonic oscillator of (bare) Hamiltonian: $$H_0=\frac{p^2}{2m}+\frac{1}{2} m \omega^2 x^2$$ (I can add to it an anharmonicity $V=\alpha x^4$ if necessary for the purpose ...
user avatar
6 votes
0 answers
91 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, ...
user avatar
  • 431
0 votes
0 answers
132 views

Molecular Docking using Quantum Computing

I would like to ask if somebody could suggest me a pair of ligand-Protein which had been validated and the corresponding resulting drug is already being used commercially. I am interested in ...
user avatar
4 votes
1 answer
183 views

Does anyone know of any good books to learn about the electronics/electrical engineering side of quantum computing?

I am a Physics student that just entered the field of quantum computing. I am obviously lacking in the electronic engineering side of things and would love to learn more! Any advice for good books?
user avatar
  • 145
2 votes
0 answers
67 views

Solution for the "Input and Output theory" for circuit/cavity-QED Quantum Architecture [closed]

This question consists of the basic calculations which are often referred to as "trivial" in most references in circuit-QED. However, are not so trivial for anyone who starts fresh into the ...
user avatar
3 votes
1 answer
66 views

Is every computer in IBM's fleet based on superconductivity?

I'm currently writing my thesis and I'd like to know which computer is based on a superconductive architecture to run some simulations. Thanks for help in advance.
user avatar
5 votes
3 answers
465 views

How are the IBM's and Google's Hadamard gates fabricated and operated?

There are thousands of articles, books and web sites describing the Hadamard Gate from a theoretical point of view. But I haven't been able to find any photo about any real implementeation of a ...
user avatar
  • 151
8 votes
2 answers
327 views

Why attenuator and not filters for QC driving line

In all the cold quantum computer designs (superconducting qubits, spin qubits) attenuators are put on the driving lines. Their role is to kill the noise spectral density that comes from higher ...
user avatar
4 votes
1 answer
110 views

STO-3G Basis Set

Can someone please explain why STO-3G is considered to be a good basis set for quantum computing, while it does not help in classical computing? I would also be very grateful for any references to ...
user avatar
1 vote
0 answers
19 views

Many-photon limit of dispersive shift Hamiltionian

In the context of superconducting quantum computing measuments, consider the dispersive shift Hamiltonian: $$ H/\hbar = \omega_R a^\dagger a + \frac{1}{2} (\omega_Q + \frac{2g^2}{\Delta} a^\dagger a)\...
user avatar
  • 1,230
2 votes
0 answers
31 views

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 ...
user avatar
3 votes
0 answers
66 views

Why are two qubits gates more noisy?

I would like to understand why two qubit gates are generally more noisy. If I am interested in single qubit gates, I can have an effective modelling as a master equation: $$\dot{\rho}=\frac{1}{i \...
user avatar
2 votes
2 answers
118 views

How does Surface-17 tell apart Z errors on Db and Dc?

I'm looking into this paper from DiCarlo's group Scalable quantum circuit and control for a superconducting surface code. I don't understand how it's supposed to identify specific single-qubit errors, ...
user avatar
1 vote
1 answer
103 views

What can be done so far with cloud quantum computing?

As a developer myself, I still do not understand what can be done so far with services like AWS BRAKET or IBM CLOUD QUANTUM COMPUTING. Can someone explain me the practical purpose of it in the present?...
user avatar
  • 23
4 votes
1 answer
641 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. ...
user avatar
3 votes
2 answers
119 views

Is there any tool for generating Hamiltonian for circuit-QED?

There are tools like QuTip helping you simulate a given Hamiltonian. However, I am wondering if is there any tool/library or something that takes e.g. a graph (G, V, E) of qubits and resonators, and ...
user avatar
6 votes
1 answer
652 views

Understanding Google's “Quantum supremacy using a programmable superconducting processor” (Part 3): sampling

In Google's 54 qubit Sycamore processor, they created a 53 qubit quantum circuit using a random selection of gates from the set $\{\sqrt{X}, \sqrt{Y}, \sqrt{W}\}$ in the following pattern: ...
user avatar
8 votes
1 answer
853 views

Understanding Google's “Quantum supremacy using a programmable superconducting processor” (Part 2): simplifiable and intractable tilings

In Google's 54 qubit Sycamore processor, they created a 53 qubit quantum circuit using a random selection of gates from the set $\{\sqrt{X}, \sqrt{Y}, \sqrt{W}\}$ in the following pattern: ...
user avatar
11 votes
2 answers
782 views

Understanding Google's “Quantum supremacy using a programmable superconducting processor” (Part 1): choice of gate set

I was recently going through the paper titled "Quantum supremacy using a programmable superconducting processor" by NASA Ames Research Centre and the Google Quantum AI team (note that the paper was ...
user avatar
3 votes
0 answers
364 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 ...
user avatar
3 votes
1 answer
752 views

How do I interpret the readout error for a quantum computer?

For example, the ibmqx2 computer has the most recent readout error of $4.40 \cdot 10^{-2}$. Does this mean per 1000 measurements, 44 faulty results exist?
user avatar
7 votes
1 answer
216 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 ...
user avatar
  • 1,230
3 votes
0 answers
45 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?
user avatar
  • 315
3 votes
0 answers
80 views

States of a qubit in a DC-SQUID

Does anybody of you know what are the two states $|0\rangle$ and $|1\rangle$ of a qubit in a DC-SQUID (2 Josephson junctions in a loop)?
user avatar