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).

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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....
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How and how much do fabrication defects affect superconducting qubit coherence time?

I used simulations to calculate T1 time of a transmon qubit, but the result is much longer than the lab data. I suspect it was because simulation does not consider fabrication defects. May I ask if ...
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what is the elementary Lab devices (and their specifications) for building superconducting qubits?

suppose I want to build a superconducting qubit, how can I find the Lab Devices and specifications which are nessecarry to build it?
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What is the charge noise in the context of superconducting qubits?

I read from some papers that the charge noise is one of the factors that cause decoherence of qubits. May I know what charge noise is and how exactly the charge fluctuation affects the qubit frequency?...
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What is the maximum and minimum value of logarithmic negativity measured for bi-party entanglement?

I have calculated logrithmic negativity for my biparty entangled system in a superconducting circuit. The negativity gives a sine curve where maximum value comes out to be 4 and minimum 0.5. Now, how ...
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Meaning of 'O_i' and 'Δ_i' terms in PulseBackend Hamiltonians

For OpenPulse enabled backends, the Hamiltonian can be retrieved via its configuration. The configuration holds a dictionary containing for example the Hamiltonian as a LaTeX string. Example code: <...
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Learning sources on cavity QED

Recently, I have been studying lecture notes on Circuit QED by Steve Girvin to learn about superconducting circuits. I am currently in the chapter about cavity QED. The description in the notes are ...
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Suggestion on reading resources on superconducting quantum computing

I am a physics student who works with NMR spin-based quantum computing, now branching into superconductor-based qubits. So I am reading lecture notes by Nathan K Langford and Steve Girvin. I can ...
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Minimal decomposition for a 4 qubit QFT in a Superconducting architecture

i'm looking for a minimal decomposition in terms of Cnot for the 4 qubit QFT circuit in the 7 qubit architecture reported in figure. I'm using qubits 0,2,4,6 as ancillas for my QPE algorithm. The ...
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Speed of Superconducting Qubit Architectures

A classical computer performs processor cycles at around 3GHz. What kind of speed should we expect (now, but also more long-term) from a quantum computer operating on superconducting qubits, such as ...
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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\...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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. ...
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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 ...
5 votes
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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 ...
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1 answer
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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?
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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 ...
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1 answer
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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\...
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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?
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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 ...
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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-...
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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 ...
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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? ...
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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 ...
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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 - ...
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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 ...
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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 ...
2 votes
1 answer
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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 &...
5 votes
1 answer
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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 ...
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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 ...
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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 ...
6 votes
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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, ...
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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 ...
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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?
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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 ...
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1 answer
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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.
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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 ...
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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 ...
4 votes
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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 ...
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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)\...
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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 ...
3 votes
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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 \...
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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, ...
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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?...
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