All Questions

Filter by
Sorted by
Tagged with
0 votes
0 answers
17 views

Why am I getting this error- "ValueError: x and y must be the same size"? If anyone knows kindly give any hint or clue to rectify it

def get_qc_for_n_qubit_GHZ_state(n): qc = QuantumCircuit(n) qc.h(0) for i in range(n-1): qc.cx(i, i+1) return qc n = 100 qc = get_qc_for_n_qubit_GHZ_state(n) qc.draw(output = 'mpl') from qiskit....
Piyush Kumar Sinha's user avatar
1 vote
0 answers
7 views

Is a molecular Hamiltonian defined uniquely? or Where do differences in pennylane Hamiltonians come from?

For a fixed fermion-qubit mapping, basis, active space, and geometry, is the electronic structure Hamiltonian uniquely defined? I would think so, since for a given basis the one- and two-body ...
a_member's user avatar
1 vote
0 answers
16 views

Effect of partial measurement on the fidelity of states

Suppose we have two pure states $|\phi_1 \rangle = \sum_i \alpha_{i,1}|i\rangle| \chi_{i,1}\rangle, |\phi_2 \rangle = \sum_i \alpha_{i,2} |i\rangle| \chi_{i,2}\rangle$ and perform a partial ...
milo's user avatar
  • 11
0 votes
1 answer
25 views

Open-source code for Lattice Surgery in STIM

I'm looking for open-source code that implements lattice surgery merging and splitting between two rotated surface code logical qubits in STIM (for d=3 or above). Whilst there are some excellent ...
ebit157's user avatar
2 votes
1 answer
41 views

Fault-tolerant CNOT gates

The controlled-not gate $$ CNOT = \begin{bmatrix}1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & 1 & 0 \end{bmatrix} $$ is important in many ...
Ian Gershon Teixeira's user avatar
2 votes
0 answers
25 views

Heisenberg picture for a quantum measurement where the outcome is recorded

I asked a related question here. From the answer by Mateus, we see that one cannot describe a quantum measurement (where the measurement outcome is recorded) as a quantum map. That is because the ...
user902020's user avatar
1 vote
1 answer
47 views

What is the quantum map that describes a measurement where the measurement outcome is known?

My question is the other case of this question. Suppose I do a measurement in the $Z$ basis with outcomes $\lambda_0, \lambda_1$ but I don't record the outcome. In this case, I can describe what ...
user902020's user avatar
2 votes
0 answers
13 views

Effective spectral gap lemma

I'm trying to understand the effective spectral gap lemma, a tool used in the context of query complexity and quantum walks. If $\Delta, \Pi$ are two orthogonal projectors and $U = (2\Pi - I)(2\Delta -...
NYG's user avatar
  • 419
1 vote
1 answer
51 views

Eigenvalues of Pauli Gate and connection to measurement

Suppose I measure a qubit in the $Z$ basis. If I measure and obtain the outcome $+1$, I get the post-measurement state $\vert 0\rangle\langle 0\vert$ and if I measure and obtain the outcome $-1$, I ...
user902020's user avatar
1 vote
1 answer
28 views

Variant of Quantum Hamming bound for CSS codes

The arguments leading to the Quantum Hamming Bound for non-degenerate $[[n,k,d = 2t+1]]$ codes $$\sum_{j=0}^t 3^j \binom{n}{j} ≤ 2^{n-k}$$ can be manipulated to find a stronger related bound for non-...
The Vee's user avatar
  • 111
0 votes
0 answers
34 views

Can't retrieve jobs for the specific (retired) manila device in ibm

I've been retrieving jobs regularly from already retired devices from ibm via the jupyter notebook without problems. Until recently, I found that I cannot access my jobs in ...
user2820579's user avatar
0 votes
0 answers
15 views

Nearest-Neighbor Depth Optimal Clifford Circuits

I am interested in the best state-of-the-art implementations for Clifford circuit compilation. In particular, I am interested optimizing the depth of nearest-neighbor $d$-dimensional Clifford Circuits....
Ben Foxman's user avatar
0 votes
0 answers
21 views

Is there a QUBO solving Q-algorithm with proven superpolynomial speedup - even for only a subclass of QUBOS?

Is there any known quantum algorithm that solves a specific subclass of QUBOs (with the subclass, I mean that certain constraints are being imposed on the QUBO model, e.g. sparsity of the QUBO matrix)...
qubitzer's user avatar
  • 838
3 votes
0 answers
43 views

Do we really apply both single-qubit and two-qubit gates in the same layer in experiments?

I'm doing experiments using superconducting computers, and my question is as follows: Performing quantum gates requires isolating the coupling between a target qubit and other neighboring qubits. To ...
jtlearner's user avatar
-1 votes
0 answers
17 views

Cosine of an operator (a+a.dag()).cosm() in Qutip does not work as it should

As mentioned in the title, the .cosm() method in QuTip fails to give the correct evolution under the Hamiltonian. I am trying to define the Hamiltonian of a non-linear LCJ circuit as follows: ...
SlothForeva's user avatar
4 votes
0 answers
29 views

Source reference for QMA-completeness of the following pairwise product of Pauli matrices

The following pairwise Pauli matrices are sufficient to capture the power of QMA complexity class. $\{I,\ I\otimes X,\ I\otimes Z,\ X\otimes I,\ Z\otimes I,\ X\otimes X,\ X\otimes Z,\ Z\otimes X, \ Z\...
Manish Kumar's user avatar
2 votes
0 answers
52 views

Confusion on the Quantum Minimum Finding Algorithm

I am a new beginner in quantum algorithms. Recently, I was trying to learn the quantum minimum finding algorithm appeared in here. I am struggling to fully understand the operations in the algorithm. ...
Robin Luo's user avatar
2 votes
0 answers
38 views

Dephasing noise and error correction

It is my impression that $ Z $ errors are the dominant source of noise in many platforms used for quantum computing. For example, Ultrahigh Error Threshold for Surface Codes with Biased Noise says ...
Ian Gershon Teixeira's user avatar
1 vote
0 answers
55 views

Super-dense coding by adding quantum correlations between classical bits

Consider the following non-local game between Alice, Bob (who are spatially separated but share a maximally entangled state) and a referee: Referee samples two question bits "$x,y$" and ...
Soham Ghosh's user avatar
0 votes
1 answer
34 views

How are ancilla qubits physically prepared and measured?

As I understand the general procedure of quantum computing: We prepare our quantum states depending on what calculation we want to do (ex: creating a spin superposition of entangled states by driving ...
PhysicsStudent101's user avatar
0 votes
0 answers
21 views

Qiskit runtime backen cannot state_preperation

I am trying to run a circuit on hardware, for that I need to initialise the state. ...
Thick Harry's user avatar
0 votes
0 answers
37 views

Is this the right code to run a QSVC algorithm on a dataset?

...
Sai Vellanki's user avatar
2 votes
0 answers
33 views

How many observables do we need to confirm a qubit state?

Suppose I have many copies of a qubit in the pure state $\vert\psi\rangle$. How many distinct observables do I need to choose to determine that I indeed hold $\vert\psi\rangle$? For example, if $\vert\...
Alber's user avatar
  • 21
3 votes
1 answer
30 views

qiskit DraperQFTAdder

my code: ...
Lexiang Xue's user avatar
-1 votes
1 answer
56 views

ModuleNotFoundError: No module named 'qiskit_algorithms'

I am doing the code migration from qiskit== 0.46.0 to qiskit==1.0 ...
Manu's user avatar
  • 59
6 votes
2 answers
818 views

Why do Bell states have all real coefficients?

Canonically, the four Bell or EPR states for 2-qubit systems are given by: $|\Phi^{\pm}\rangle = \frac{1}{\sqrt{2}} \left( |00\rangle \pm |11\rangle\right)$ $|\psi^{\pm}\rangle = \frac{1}{\sqrt{2}} \...
Danyel's user avatar
  • 63
3 votes
1 answer
51 views

How does one identify Pauli logicals in a hyperbolic surface code?

I understand how the Pauli X and Z logicals on the planar surface code work - they are stringlike operators between either the rough boundaries (in case of the Z logical) or between smooth boundaries (...
clearski's user avatar
1 vote
1 answer
53 views

How to interpret the product of POVM elements?

Suppose $m\not=n$, and fix a state $|\psi\rangle$. If $\\{P_k\\}$ defines a PVM, then we have $\langle \psi|P_n P_m|\psi \rangle = 0$. Physically, this makes sense, as one cannot obtain two different ...
Solarflare0's user avatar
0 votes
0 answers
31 views

Finding stabilizers from a T distillation code

Consider $T$ state distillation as per Figure 14 in this paper. I am trying to figure out what the stabilizers are. I thought of trying to evolve them starting from e.g. $S = XI\cdots I$ acting on the ...
Johnathan's user avatar
  • 101
2 votes
2 answers
282 views

In exercise 8.23 of Nielsen and Chuang why is the quantum operation no longer trace-preserving?

My question is about this exercise from Nielsen & Chuang: For context, $\mathcal{E}_{AD}$ is the quantum operation for amplitude damping on a single physical qubit, with operation elements given ...
David's user avatar
  • 23
0 votes
1 answer
41 views

Quantum Cryptography without Bell's Theorem -- Brassard - Bennett - Mermin

It is an old paper but I'm trying to understand one of their argument. They say that if $$U|u\rangle |a\rangle = |u\rangle |a^\prime\rangle \ \ \ \mathrm{and} \ \ \ U|v\rangle |a\rangle = |v\rangle |a^...
JMark's user avatar
  • 173
1 vote
1 answer
31 views

Computing expectation of a SparsePauliOp using StateVector

I have a SparsePauliOp object $H$ acting on $N = 21$ qubits, and a statevector $|\psi \rangle$ acting on $N=21$ qubits. I need the expectation of $H$ using this state $|\psi \rangle$: $$\langle H \...
Soumyadeep sarma's user avatar
1 vote
0 answers
30 views

Extracting syndromes by measuring gauge operators in subsystem codes

In subsystem codes, it is well-known that we can extract syndromes by measuring some gauge operators, instead of measuring stabilizers. For example, if a stabilizer $s$ is a product of gauge operators ...
lan's user avatar
  • 61
2 votes
1 answer
60 views

Beyond polynomial speedups in diagonal entries estimation

Consider the task of estimating the diagonal entries of the power of a real sparse matrix A with $N = 2^n$ rows: Input: $A \in \mathbb{R}^{N \times N}$ with $A = A^\top$ and $s$-sparse and row-...
incud's user avatar
  • 763
0 votes
0 answers
19 views

Process Tomography and transpiler not running and eventually crashing kernel

I am running a Quantum Process Tomography on a circuit with a custom pulse added to a calibation for a CNOT gate. Upon running the circuit, running it on the backend takes forever and eventually ends ...
idislikecoding's user avatar
2 votes
1 answer
71 views

Why do we use Z-gates in the following figure?

This is a picture of a 'T-gate gadget' and a proof for a circuit from “Quantum homomorphic encryption for circuits with low T-gate complexity” by Broadbent, Jeffrey (2015) (arXiv). My question is why ...
yuria20's user avatar
  • 31
0 votes
0 answers
27 views

State of the art stabilizer decomposition quantum circuit simulators - Suggestions

I've programmed an algorithm which decomposes a quantum circuit $U$ (and given initial state $|s\rangle$) into a sum of $N$ stabilizer states $|\phi_i\rangle$: $ \begin{equation} U|s\rangle=|\psi\...
schmector's user avatar
0 votes
1 answer
26 views

Doubly stochastic gradient descent on pennylane

H = 4+2I⊗X+4I⊗Z−X⊗X+5Y⊗Y+2Z⊗X. I am given this Hamiltonian which I want to minimize using doubly stochastic gradient descent, and the code that I found on pennylane website is: ...
Kutubkhan Bhatiya's user avatar
2 votes
1 answer
49 views

$[[10, 2, 2]]$ codes with transversal T gates

There is a 10-to-2 magic distillation protocols for the $T$ state based on the four-qubit codes (https://arxiv.org/pdf/1204.4221). As the protocol has order-2 distillation efficiency, we can use a $[[...
Yunzhe's user avatar
  • 871
3 votes
1 answer
65 views

How to calculate guessing probability for quantum key distribution?

There are 3 Projections $P_1$, $P_2$, and $P_3$ corresponding to 3 inputs $x = 1, 2, 3$ for Alice. Similarly, the same projections are used by Bob for $y = 1, 2, 3$. Each input has 2 outcomes, $a = 1, ...
alpacino's user avatar
3 votes
1 answer
69 views

What exacly is passManager and passes in qiskit?

I am trying to understand what exactly is passManager, what exactly it its use, where exactly we need to use it? https://github.com/Qiskit/qiskit-tutorials/blob/...
Manu's user avatar
  • 59
3 votes
1 answer
157 views

What's so bad about preparing magic states by measuring Clifford gates?

Suppose we want to perform a gate from the third level of the Clifford hierarchy for example $ T,CS, CCZ, CCX $. To implement such a gate using gate teleportation we need to take as an input certain ...
Ian Gershon Teixeira's user avatar
0 votes
1 answer
60 views

generating pure errors (destabilizers) by given stabilizer and logical group

Suppose we have a stabilizer code on n physical qubits, with stabilizer group S and assume fixed representatives of the logical operators L. Given this fixed set of generators for S and L, can we ...
reza's user avatar
  • 11
0 votes
1 answer
30 views

What are existing ways to do logical CZ gates on the surface code?

The surface code is a CSS code, so assuming all-to-all connectivity (unrealistic on most physical platforms), the logical CNOT can be implemented transversally. In a biplanar architecture, the setup ...
clearski's user avatar
0 votes
1 answer
68 views
+50

How to implement Pauli Twirling error mitigation technique in qiskit?

I am studying the error mitigation techniques. There is one technique of error mitigation called as pauli twirling. I need some toy code of qiskit which can show ...
Manu's user avatar
  • 59
0 votes
1 answer
25 views

A question on dimensions of the basis vectors for the $[[6,4]]$ code

I am working from page $8$ of this paper. The generator for the coset representatives of $C^{\perp}$ in $C$ for the $[6,5,2]$ classical code is given by $$G_{C/C^{\perp}} = \begin{bmatrix} 1 & 1 &...
am567's user avatar
  • 641
0 votes
0 answers
33 views

Can an $n$-qubit observable be constructed from single-qubit Pauli X and Z observables? [duplicate]

Any $2\times2$ matrix can be expressed as the sum and product of the identity, Pauli $X$ and Pauli $Z$ matrices. This is often used to express a singe-qubit state using just Pauli matrices. One can ...
Alfred Huang's user avatar
-1 votes
0 answers
24 views

POVM and non distinguishibility

The fact that non orthogonal states can't be distinguished is the reason why Alice can't communicate information faster than the speed of light when they have a qubit each and they are in bell state ...
Aashish J's user avatar
1 vote
1 answer
45 views

Unital qubit channels as a convex combination of entanglement-breaking and unitary channel

I am trying to show that for $T:B(\mathbb{C}^{2})\rightarrow B(\mathbb{C}^{2})$ a unital qubit channel, that T is a convex combination $T=pB+(1-p)Ad_{V}$, where B is a Entanglement-Breaking(EB) ...
Pink Elephants's user avatar
0 votes
0 answers
24 views

Reference Implementation for Circuits in 1801.01081 [HIGH PERFORMANCE QUANTUM MODULAR MULTIPLIERS]

I am currently working on my own quantum arithmetics project and I cannot seem to get my version of Fig. 5 and Fig. 6 from https://arxiv.org/pdf/1801.01081 to work. (And it's not because of the ...
LukasM's user avatar
  • 53

15 30 50 per page
1
2 3 4 5
238