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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How to determine the single-qubit phase?
In some works it is suggested to find the qubit phase by the following method:
Apply $X/2$ (or $Y/2$) gate - preparing the qubit in superposition.
Detune the qubit by flux pulse, for example here ...
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I would like to know the textbook/paper on hamiltonian for rf-SQUID
I am a graduate student in the Department of Computer Engineering, and I am currently doing research on superconducting quantum computers. In particular, I am focusing on quantum annealing machines ...
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Which HEMT (standard transistor) amplifiers are used in superconducting qubit readout chain?
The two images below show HEMT amplifiers at the 3-6K stage. All the papers simply mention "standard HEMT amplifiers", but I am not sure what "standard" means. Does anyone know of ...
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study quantum hardware
I want to start studying quantum hardware, in particular I'm interested on superconducting qubit. Are there any valid resources for a beginner (notes, lecture...)? I'm an electronic engineer and I ...
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Phase accumulation for multiple Rabi driving pulses
When a single-qubit gate is operated by Rabi driving, the resulting operator is equivalent to
$$ \hat{O} = R_z(\omega t) R_x(\Omega t)\tag{1}$$
where $\omega$ is the frequency of the driving field, $\...
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Why superconducting qubits need periodic calibration?
I want to understand in some detail why superconducting qubits need periodic calibration. The usual, hand wavy explanation is environmental effects that tend to vary. However, I suspect that the ...
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In qubit phase tracking, does the phase $\delta$ have to be synchronized to the Larmor precession?
In many textbooks (e.g. LaPierre 2021 or Byrd 2022), when dealing with the physical implementation of quantum gates in spin qubits, Larmor precession is usually introduced first as a way to rotate the ...
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What is the clear definition of coherent versus incoherent errors?
The noise types in quantum computing are pivotal topics frequently discussed in academic papers.
Could you provide a clear definition of coherent versus incoherent errors? Additionally, I'm keen to ...
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What is the optimal hardware for quantum computing, and what factors contribute to its preference?
In conventional computing, the use of CMOS (Complementary Metal Oxide Semiconductor) technology as the foundational circuitry for digital logic gates in CPUs has become the industry norm. CMOS's ...
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Quantum Crosstalk in gate scheduling with different gates
I am working on quantum crosstalk, specifically on CNOT and SWAP gate operations that lead to crosstalk. I have encountered works that decompose CNOT and SWAP with iSWAP and CZ gates. I would like to ...
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What is a "quantum communication link"?
The IBM roadmap for scaling their quantum computers refer to a quantum communication link to combine together multiple smaller quantum chips. What is the technology that enables connecting together ...
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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 ...
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Could you use $|0\rangle$ as excited state and $|1\rangle$ as ground state in transmon?
Why is the $|0\rangle$ state usually taken to be the ground state of a transmon qubit, and the $|1\rangle$ state the first excited state? Could you reverse this, and if so how would it affect the ...
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How to estimate the losses of a transmon qubit to its flux bias line
For transparency, I also posted this at the physics stackexchange, but it might be more fruitful to discuss here.
Already in the original transmon paper by Koch et al. is it stated that while the ...
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Low yield rate of superconducting QPU fabrication?
What percentage of superconducting QPU chips are discarded after fabrication because of high error rate? Are some physical qubits significantly bad in state of the art superconducting QPUs? Are these ...
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Do Majorana qubits have a future?
There are still major efforts to observe Majorana Fermions in condensed matter systems (most recently this paper), with the ultimate goal of using topologically protected Majorana qubits for quantum ...
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How to represent two gates addition on Qiskit composer. we can do tensor product and multiplication but how to do Addition
How to represent two gates addition on Qiskit composer we can do it in python code by using qiskit library but I would like to visually see how addition of two operators look like in composer.
I am ...
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Is it possible to separate a quantum circuit into several small sub circuits and measure individually?
For example, if I have a BV3 circuit and I execute and measure them together, the results are 100% 111.
If I separate it into three subcircuits and measure only one qubit each time, the measurement ...
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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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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 ...
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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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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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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 ...
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