Questions tagged [foundations]
For questions about quantum foundations. Examples include questions about fundamental axioms, interpretations, contextuality, or generalized probabilistic theories.
37 questions
0 votes
0 answers
39 views
Reproducing the PBR theorem on IBM hardware: is the wavefunction “real” even on noisy qubits?
I’ve been exploring whether the quantum state (ψ) represents information or reality by trying to replicate the Pusey–Barrett–Rudolph (PBR) test in Qiskit. The recent preprint Yang, Yuan & Barnes (...
- 1,371
2 votes
0 answers
84 views
Can quantum coprograms exist?
Some papers mention that not all classical programming abstractions (like conventional conditional jump and the $\lambda$-calculus) can be correctly implemented on quantum computers. The paper also ...
- 121
0 votes
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140 views
Proof of Theorem 3 of Frenkel, and Weiner, Commun. Math. Phys. 340, 563 (2015)
Suppose Bob performs a $k$-outcome measurement, characterised by the POVM $E = \{E_j\}_{j=1}^k$, on $l$ qudits $\{\rho_i\}_{i=1}^l$ sent by Alice. This results in an $k \times l$ column-stochatstic ...
- 165
2 votes
1 answer
99 views
How quantum laws hold on macroscopic level in classical computers?
Disclaimer: I am not sure about whether my question is suitable for here, but I will ask it anyway. I am making research about quantum cryptography, so I start reading a book. In one paragraph, it is ...
7 votes
2 answers
252 views
Can we think that any multi-qubit quantum gate has a constant complexity from physics perspective?
It's known that any multi-qubit quantum gate can be represented as a product of a number of CNOT and single-qubit gates. The total number of these simple gates required is exponential (in the number ...
- 8,201
6 votes
2 answers
548 views
Prove that if Kraus operators of $\Phi$ form an ONB then $\Phi$ is the replacement map
This problem is from a "passing remark" in this lecture notes. With the help of some colleagues I managed to find a way for this supposedly elementary fact, but I would like to see if there ...
4 votes
3 answers
269 views
What is the computational power of classically mixed states?
It is my understanding that mostly one considers as the "classical" state, a single bit string (eg 00101), with a discrete number of deterministic gates applied to it. All computers that ...
- 311
3 votes
1 answer
392 views
What are the postulates of Continuous Variable Quantum Computing?
I am a computer scientist. When I learned quantum information for the first time (in the circuit model, with qubits), I was presented four postulates that described mathematically (i) the possible ...
- 927
2 votes
0 answers
82 views
What is a simple example of Spekken's measurement contextuality?
Kochen-Specker theoreom (1967) established the notion of contextuality which is usually termed as KS-contextuality. Spekken (2005) generalizes the definition of contextuality. Spekken introduces three ...
- 321
6 votes
2 answers
2k views
Doing non-unitary operations on quantum computer
So I am trying to implement non-unitary operations on Qiskit. There is an option to perform conditional operations in Qiskit. Suppose I prepare a qubit state in superposition. $|\psi\rangle=\sqrt{\...
- 408
2 votes
1 answer
349 views
De-coherence and Wigners friend?
So in the thought experiment Wigners friend the paradox is ultimately due to a difference of descriptions of density matrices. If the physical variable that is measured of the spin system is denoted ...
- 437
7 votes
1 answer
757 views
What are the 2022 Nobel Prize winning papers of Alain Aspect, John Clauser, and Anton Zeilinger, and how do they fit into the timeline of QIS?
The 2022 Nobel Prize in Physics was awarded to Alain Aspect, John Clauser, and Anton Zeilinger for "experiments with entangled photons... pioneering quantum information science". Presumably ...
1 vote
1 answer
103 views
How can a "state" in a contextuality scenario be contextual?
As also discussed in the answers to What do noncontextual scenarios with no quantum model represent? and Can the Peres-Mermin square be reframed as a statement on the associated conditional outcome ...
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- 27.9k
4 votes
1 answer
114 views
Why coherence measure monotonicity under selective incoherent operation should be form $C\left( \rho \right) \ge \sum_n{p_nC\left( \rho _n \right)}$?
In this paper, the authors give four postulates if a function $C$ can be taken as a coherence measure: (C1) $C(\rho) \geqslant 0$, and $C(\rho)=0$ if and only if $\rho \in \mathcal{I}$, where $\...
- 745
3 votes
1 answer
402 views
Can joint measurement be achieved in two labs far apart?
Consider the following scenario: Alice and Bob are in two labs far apart, and they each have one qubit. Can joint measurement (for bipartite projective measurement, they are measurements that cannot ...
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