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How to get started with the Alibaba Cloud Quantum Computing Service?
According to this press announcement from March 1st 2018, the Alibaba Cloud offers access to an 11 qubit quantum computer via their cloud services. Quote:
Alibaba Cloud, [...] and Chinese Academy of Sciences (CAS) [...] have launched the…
blalasaadri
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16
votes
3 answers
How to construct matrix of regular and "flipped" 2-qubit CNOT?
When constructing the matrices for the two CNOT based on the target and control qubit, I can use reasoning:
"If $q_0$==$|0\rangle$, everything simply passes through", resulting in an Identity matrix style $\begin{bmatrix}1&0\\0&1\end{bmatrix}$ in…
Thomas Hubregtsen
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16
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State of the art gate speeds and decoherence times
I am interested in the state of the art gate speeds and decoherence times for the qubit types I know are being pursued by companies presently:
superconducting qubits,
ion trap qubits,
photonic qubits.
Where can I find these, and is there a place…
user1271772 No more free time
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16
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6 answers
How to construct a multi-qubit controlled-Z from elementary gates?
For the implementation of a certain quantum algorithm, I need to construct a multi-qubit (in this case, a three-qubit) controlled-Z gate from a set of elementary gates, as shown in the figure below.
.
The gates that I can use are
the Pauli gates…
Dyon J Don Kiwi van Vreumingen
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16
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2 answers
How would a quantum computer be used to solve Partial Differential Equations?
Say you have a PDE you want to solve.
What kind of quantum algorithms would you use to solve it?
How do we input our problem on a quantum computer?
What will be the output and in what form?
I know that quantum algorithms for solving linear systems…
cnada
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16
votes
2 answers
What's the Difference between T2 and T2*?
$T_2$ generally refers to the measurement of the coherence of the qubit with respect to its dephasing (that's a rotation through the $|0\rangle$ - $|1\rangle$ axis of the Bloch sphere for those of us visualizing). But sometime in the literature,…
psitae
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16
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Violation of the Quantum Hamming bound
The quantum Hamming bound for a non-degenerate $[[N,k,d]]$ quantum error correction code is defined as:
\begin{equation}
2^{N-k}\geq\sum_{n=0}^{\lfloor d/2\rfloor}3^n\begin{pmatrix}N \\ n\end{pmatrix}.
\end{equation}
However, there is no proof…
Josu Etxezarreta Martinez
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16
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3 answers
Are there any estimates on how complexity of quantum engineering scales with size?
It seems to me that an extremely relevant question for the prospects of quantum computing would be how the engineering complexity of quantum systems scales with size. Meaning, it's easier to build $n$ $1$-qubit computers than one $n$-qubit computer.…
Keith Rush
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16
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Building a quantum computer in simulation
If one wants to start building a quantum computer from scratch inside simulations (like how people get to build a classical computer from scratch in the Nand2Tetris course), is it possible?
If yes, what would be some possible approaches?
Also, what…
ak_nama
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16
votes
1 answer
What is the difference between QAOA and Quantum Annealing?
Edward Farhi's paper on the Quantum Approximate Optimization Algorithm
introduces a way for gate model quantum computers to solve combinatorial optimization algorithms. However, D-Wave style quantum annealers have focused on combinatorial…
hopefully coherent
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16
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What is the physical representation of a qubit?
In regular computers, bits may be physically represented using a wide variety of two-state devices, such as polarity of magnetization of a certain area of a ferromagnetic film or two levels of electric charge in a capacitor.
But qubits have a…
user609
16
votes
2 answers
Representation of real numbers in quantum computers
In classical binary computers, real numbers are often represented using the IEEE 754 standard. With quantum computers you can of course do this as well - and for measurements this (or a similar standard) will probably be necessary since the result…
blalasaadri
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15
votes
2 answers
Does higher channel fidelity imply higher entanglement fidelity?
Consider two noisy quantum channels (CPTP maps), $\Phi_1^A$ and $\Phi_2^A$, acting on a system $A$. Suppose that for any pure state $\left|\psi\right>\in \mathcal H_A$,
$$
F\big(\psi, \Phi_1^A(\psi)\big) \geq F\big(\psi,…
UncertainTea
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15
votes
2 answers
How many two-qubit gates are required to implement a general N-qubit unitary?
Is there a known formula or a scaling behaviour for how many two-qubit gates are required to construct a general N-qubit unitary?
I suppose there are several cases to consider:
Exact representation of the gates
Approximate decompositions to a given…
as2457
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15
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6 answers
Is there any online Bloch sphere simulator?
While writing this answer I realized it would be really helpful if I could show the OP a video or .gif of how qubit states in Bloch spheres transform under certain unitary operations. I googled up a bit and could find only these two…
Sanchayan Dutta
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