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1500 questions
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Is it essential to apply Quantum Singular Value transformation twice for Hamiltonian simulation?
I have been reading the paper A Grand Unification of Quantum Algorithms and I need clarification on the Hamiltonian simulation algorithm provided in the paper on page 23. . In procedure part point 2 says apply QSVT twice. I am confused here. Does…
Shashi Kumar
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State of the art decoding algorithms for surface code
I am interested to know what are the "most promising" decoder algorithms that are used in surface code today.
Of course, different criteria can tell what we expect from a good decoder. In particular, we would like it to:
Be fast
Have a high…
Marco Fellous-Asiani
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6
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2 answers
Proven quantum advantage (in the algorithmic sense) without error correction (for specific algo, or noise models)
I would like to know if there are some specific class of quantum algorithms, under some hypotheses about the noise model behind the quantum gates for which we know that there is an exponential advantage in the presence of noise.
What I mean by that…
Marco Fellous-Asiani
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Verification of local unitary equivalence between two pure states
This might be a non-trivial and hard problem. I've been thinking about this for days but couldn't find a good answer, so I hope any of you could give me a good answer/intuition for me to move forward.
Suppose I have two pure states each being $n$…
userflux9674
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6
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3 answers
does CNOT gate cause entanglement?
I have just started learning Quantum computing.
Pairs of qubits that are “entangled,” which means the two members of a pair exist in a single quantum state. Changing the state of one of the qubits will instantaneously change the state of the other…
Vinay Sharma
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6
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1 answer
Can separable states have quantum mutual information larger than one?
Consider bipartite (qubit) systems. The classical mutual information between a pair of binary
registers,
$$I(X:Y)\equiv H(X)+H(Y)-H(X,Y),$$
is always lesser than $1$ (and non-negative). On the other hand, the quantum mutual information of a…
glS
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6
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2 answers
How do we know a "quantum function call" is worth the same amount of time as a "classical function call?"
In quantum and classical algorithms, we often need to do "function calls." Quantum algorithms such as Grover's algorithm or the Deutsch–Jozsa algorithm can take a fewer number of function calls than their classical counterparts, and this is often…
Maximal Ideal
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How exactly is the stated composite state of the two registers being produced using the $R_{zz}$ controlled rotations?
This is a sequel to How are two different registers being used as "control"?
I found the following quantum circuit given in Fig 5 (page 6) of the same paper i.e. Quantum Circuit Design for Solving Linear Systems of Equations (Cao et al.,2012). …
Sanchayan Dutta
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What measures can be taken against attacks on cryptosystems by quantum computers other than just classifying research?
If quantum computers advance to the point where they can defeat RSA, DSA, SHA (and really all existing classical public key encryption or and authentication) then it appears that it would be impossible to make secure transactions on the internet. …
user4574
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6
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3 answers
Reverse Quantum Computing: How to unmeasure a qunit
After taking some measure, how can a qunit be "unmeasured"? Is unmeasurement (ie reverse quantum computing) possible?
user820789
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What classical public key cryptography protocols exist for which hacking is QMA complete or QMA hard?
Such a public key cryptosystem would be "quantum safe" in the sense that quantum computers cannot efficiently solve QMA hard problems.
user1271772 No more free time
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6
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What are examples of the correspondence between channels and their Stinespring dilations?
In this post I read that
"quantum measurements are special cases of quantum channels (CPTP maps). Stinespring's dilation states that any quantum channel is realized by partial tracing a unitary operator acting on a possibly bigger Hilbert space."
Is…
Naima
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How linear combination of unitaries gradient work (Qiskit, PennyLane)?
I'm trying to implement linear combination of unitaries(LCU) gradient from Qiskit Gradient Framework
but on PennyLane.
First, i looked through the source code in Qiskit.
In Qiskit LCU gradient if we have 2 parameterized gate and 2 hamiltonian terms…
Natchapol Patamawisut
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Measuring ancillas in Shor's algorithm
When considering Shor's algorithm, we use ancilla qubits to effectively obtain the state
$$\sum_x \left|x,f(x)\right>$$
for the function $f(x) = a^x \mod N$.
As I have learned it, we then measure the ancilla qubits, to obtain, say $f(x) = b$ and get…
nippon
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6
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3 answers
Transforming a Quantum State to a superposition of its inverse
Does there exist a circuit that allows you to transform a quantum state into a superposition of its inverse; i.e., transform a state into an equal superposition of all basis states that are orthogonal to the initial state?
For example…
John Burke
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