Questions tagged [qudit]

For questions mainly related to qudits, the unit of quantum information in d-level quantum systems.

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Hadamard gate for qudit (dimesion 8)

I am using the code for generating the gates for qu8it The resultant gate is not unitary (and so not hermitian too). I am a bit confused with the result. Is it possible for a quantum gate to be non-...
quest's user avatar
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5 votes
1 answer
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Qudits in NISQ Devices: Benefits Beyond Dimensional Advantages?

It's clear from foundational research that qudits can provide an enhanced control of the Hilbert space over qubits, and I've encountered references that highlight improved robustness and noise ...
banercat's user avatar
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Is it possible to convert a qudit to a qubit?

I am trying to write a Qiskit code for a algorithm which uses qudits. I want to use qubits instead because $p$ value can go pretty high. Is it mathematically possible to convert qudit to qubit for ...
videet.acharya's user avatar
1 vote
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74 views

Application of transformation $U_d$ that maps any qudit state to $|d-1\rangle$

When giving examples of universal gate sets in the paper Qudits and High-Dimensional Quantum Computing, the authors first define the transformation that maps any given qudit state to $|d-1\rangle$: $$ ...
banercat's user avatar
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Help to make the equations of state of qubits?

.., and find their cofacents, after H(q1) ->CNOT(q1,q2) -> H(q2) On the website https://algassert.com/ The preparation is like this. I understand so far The preparation is like this. I ...
Даниил Данилов's user avatar
5 votes
0 answers
81 views

Smallest qudit error correcting/detecting codes

Consider encoding a qubit into $n$ qubits. It is well known that the smallest error detecting code is in $n=4$ qubits and the smallest error correcting code is in $n=5$ qubits. Is there a similar ...
Eric Kubischta's user avatar
3 votes
1 answer
78 views

Cirq seems to output 0 instead of |2> with qutrits

I am experimenting a bit with qutrits on Cirq and came across a problem: my output is 0 when it should be |2>. I defined my qutrit as follows: ...
Q.Ask's user avatar
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The operator of the composite system given the operator of the single system

Define the operator on a qudit system as \begin{align} o &= \sum_{s, s^\prime=1}^d o_{s,s^\prime}\vert s\rangle\langle s \vert \otimes \vert s^\prime\rangle \langle s^\prime \vert. \tag{1} \end{...
Michael.Andy's user avatar
2 votes
0 answers
42 views

qudits vs bipartite system states [duplicate]

Suppose we have a bipartite system of two qubits. It will form a 4d hilbert space. Also, suppose I have just one quantum system and it is a 4-level system. It will also form a 4d Hilbert space. What ...
Chetan Waghela's user avatar
1 vote
1 answer
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Two Qudit custom gate error in Cirq

I am trying to build two qudit CX (d-dim) gate. and getting below error. There is no issue in the unitary matrix. Please suggest to resolve the error.
SDubey's user avatar
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Interpretation of Qudit measurement output in cirq

Here [+1] represents X gate for qutrit. How the Counter value is coming to 5? which is the measurement outcome(q0q1q2->102). Even for (q0q1q2->101) also counter value is 5. In total, for this 3 ...
SDubey's user avatar
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130 views

Is the post-measurement state always pure after a partial measurement?

Imagine I have two potentially entangled qudits and measure the first one using some Hermitian operator $M$ that has only one eigenstate per eigenvalue and get some outcome $m$. Can I know for sure ...
learner's user avatar
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4 votes
3 answers
570 views

Are there qudit systems, and why are they not as popular as qubit systems?

Qudit is a $d$-level system that generalizes a qubit. From what I understood qudits are more resource efficient when it comes to spanning the state space. If $N$ is a dimension of a state space, then ...
MonteNero's user avatar
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2 votes
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How do I generate gates for qudits with $d=4$?

So I was working on a project with qudits (specifically d = 4) and came across a problem. How do I generate gates for these? I can construct Hadamard and X gates for these, but how does one approach ...
Random's user avatar
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Can we rotate Bloch vectors for qudits like we do with qubits in the Bloch sphere?

I have been looking into the Bloch vectors for qudits and have been wondering if we can do rotations that are similar to the rotations in the qubit Bloch sphere. Like, once we create a Bloch vector ...
Parmeet Singh EP 066's user avatar
5 votes
1 answer
313 views

What is the relation between a Fock state and a qudit?

What is the relation between a Fock state and a qudit? Is the Fock state $|n\rangle, n=0, 1, 2, ...$ a qudit having $d=\infty$?
incud's user avatar
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Uniformly distributed state in the Weyl basis

The Weyl basis (also known as Weyl-Heisenberg) is an orthonormal, unitary, and non-Hermitian basis for the Hilbert space of dimension $d$. The basis elements are given by $$ U_{ab} = \sqrt{\omega^{ab}}...
Mateus Araújo's user avatar
2 votes
1 answer
633 views

Implementing quDit algorithms in Qiskit using quBit

How do you implement any $d$-dimensional qudit circuit in qiskit using qubits to simulate on an actual quantum computer?
Ironman's user avatar
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Why `cirq` needs `Qid` class instead of just `Qudit` class?

I am just wondering in what way cirq.Qid class generalizes qudits. From cirq.Qid documentation we read that it Identifies a ...
Fallen Apart's user avatar
4 votes
1 answer
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Canonical construction of Logical Fourier Gate

For physical $d$-dimensional qudits we can define $$X= \sum_{i=0}^{d-1} |i+1\rangle \langle i |$$ and $$Z = \sum_{i=0}^{d-1} \omega^i |i\rangle \langle i |,$$ with $\omega=e^{2\pi i/d}$. The Fourier ...
M. Stern's user avatar
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How does the NOT gate generalize beyond binary?

If we are working with qudits instead of qubits, how do the NOT and CNOT gates work? If the control state for a qubit system is $|1\rangle$, what is it for a $d$-ary qudit system, and why? For ...
Sam's user avatar
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How to generalize the relationship HXH = Z for higher dimensions

Concerning the Hadamard gate and the Pauli $X$ and $Z$ gates for qubits, it is straightforward to show the following relationship via direct substitution: $$ HXH = Z.\tag{1}$$ And I would like to ...
Coconut's user avatar
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Is the column vector of a uniformly sampled random unitary matrix a uniformly sampled random state vector?

I am wondering if a random unitary matrix taken from a Haar measure (as in, it is uniformly sampled at random) can yield a uniformly sampled random state vector. In section 3 of this paper it says &...
Quantum Guy 123's user avatar
2 votes
1 answer
172 views

How does $U_f$ act on a qudit state in the Deutsch-Jozsa Algorithm

The problem starts with the given the input state $|\psi_{in} \rangle = |0 \rangle |1 \rangle$, I'm asked to calculate $|\psi'\rangle = H_d \otimes H_d |\psi_{in} \rangle$ where $H_d$ is the Hadamard ...
jmacuna's user avatar
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Fault-tolerant qudit computation: advantage? [closed]

What are advantages of a fault-tolerant qudit computation compared with fault-tolerant quantum computation for qubits?
Chloé.X.AI's user avatar
3 votes
1 answer
239 views

Can a single qutrit in superposition be considered entangled?

Often in quantum computing the idea of quantum superposition is introduced well before the concept of entanglement. I suspect this may be because our conception of (classical) computing privileges ...
Mark Spinelli's user avatar
2 votes
1 answer
120 views

How to simulate spin-1 systems with qiskit or on the IBMQ platform?

I am wondering how to simulate spin-1 systems with qiskit or on the IBMQ platform? I want to initialize a qudit (a spin-1 system), and then define the usual operations (such as Sx, Sy, and Sz) on the ...
Debasish Banerjee's user avatar
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Find the qutrit analogue of certain qubit and ququart formulas of Li and Qiao for testing separability

In eqs. (33), (43)-(46), (56) of their paper, "Separable Decompositions of Bipartite Mixed States" https://arxiv.org/abs/1708.05336, Li and Qiao present a number of formulas pertinent to testing the ...
Paul B. Slater's user avatar
8 votes
1 answer
352 views

$n$ qubit vs. a $d=2^n$ qudit states and measurements

The pure states of a qudit inhabit the $\mathbb{CP}(d-1)$ manifold. Is it true that the pure states of $n$ qubits live on the $\mathbb{CP}(2^n-1)$ manifold? If the answer to the first question is yes, ...
mavzolej's user avatar
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4 votes
1 answer
79 views

Explicit 16⨯16 matrix representations of two-qudit entanglement witnesses

I have a set of $16 \times 16$ two-qudit density matrices. I would like to study the bound-entanglement for this set, making use of entanglement witnesses for which explicit matrix representations are ...
Paul B. Slater's user avatar
3 votes
1 answer
114 views

Computing with qutrits

I'm doing some calculations with qutrits and I need a unitary matrix $U$ that does the following: $$U|00\rangle = |12 \rangle - | 21\rangle $$ $$U|11\rangle = |20 \rangle - | 02\rangle $$ $$U|22\...
Apo's user avatar
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6 votes
0 answers
191 views

Why can a point in anti-de Sitter space be modeled as a logical qutrit and how is its error correction done?

This isn't my area but the recent Quanta article How Space and Time Could Be a Quantum Error-Correcting Code struck me as interesting. They mention: In their paper[1] conjecturing that holographic ...
Sanchayan Dutta's user avatar
10 votes
4 answers
1k views

How is quantum teleportation generalized to qudits?

In an answer to a previous question, Generalization for n quantum teleportations, Craig Gidney states: The more complicated way to generalize teleportation is figuring out how to make it work on ...
user820789's user avatar
  • 3,302
4 votes
2 answers
293 views

Time-bin encoding qudits

Time-bin encoding is a technique used in Quantum information science to encode a qubit of information on a photon. Wikipedia Is there a generalization for $n$-th level qudits?
user820789's user avatar
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3 votes
1 answer
412 views

Graph state and maximally entangled state

How can I show that a multi-qudit graph state $|G\rangle$ is the maximally entangled state? What kind of measure of entanglement can be used to quantify the amount of entanglement in a given graph ...
Popov's user avatar
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3 votes
2 answers
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Combining Different Qunits

Has any work been done on quantum systems which use a combination of types of qunits (eg. using qubits & qutrits simultaneously)? If work has been done, what kind of work has been done? (eg. in ...
user820789's user avatar
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3 votes
2 answers
309 views

Hilbert space to accurately represent 3x3 Rubik's Cube

What Hilbert space of dimension greater than 4.3e19 would be most convenient for working with the Rubik's Cube verse one qudit? The cardinality of the Rubik's Cube group is given by: Examples 66 ...
user820789's user avatar
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5 votes
2 answers
408 views

Computing with Logical Qunits

What exactly is a logical (non-physical? error corrected?) qunit? Can quantum systems be built exclusively w/ logical qunits?
user820789's user avatar
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9 votes
1 answer
315 views

Does local Clifford equivalence have a direct graphical representation for qudit graph states of non-prime dimension?

This question is a follow-up to the previous QCSE question: "Are qudit graph states well-defined for non-prime dimension?". From the question's answer, it appears that there is nothing wrong in ...
SLesslyTall's user avatar
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6 votes
3 answers
2k views

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's user avatar
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11 votes
1 answer
271 views

Are qudit graph states well-defined for non-prime dimension?

Qudit graph states are $d$-dimension generalisations of qubit graph states such that each state is represented by a weighted graph $G$ (with no self-loops) such that each edge $(i, j)$ is assigned a ...
SLesslyTall's user avatar
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3 votes
2 answers
308 views

How to represent a qubyte?

I was not able to locate any visuals online. The visual I have in my head is a cube w/ bloch spheres as the eight vertices. I am also curious about a matrix representation, although I am not sure ...
user820789's user avatar
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3 votes
2 answers
2k views

Difference between 3 qubits, 2 qutrits & 1 six level qunit

What is the difference between 3 qubits, 2 qutrits and a 6th level qunit? Are they equivalent? Why / why not? Can 6 classical bits be super-densely coded into each?
user820789's user avatar
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10 votes
2 answers
1k views

How to show whether a bipartite high-dimensional system is entangled?

"How do I show that a two-qubit state is an entangled state?" includes an answer which references the Peres–Horodecki criterion. This works for $2\times 2$ and $2\times3$ dimensional cases; however, ...
user820789's user avatar
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4 votes
1 answer
113 views

What are the differences between "$n$-th level e-bits" and "$n$-th level qunits"?

I have seen qubits, qutrits & entangled bits (e-bits) a decent amount. I have also seen qunits/qudits for n-th level qubits. What I am trying to wrap my head around is the differences between n-th ...
user820789's user avatar
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9 votes
2 answers
411 views

Do any specific types of qudits other than qubits and qutrits have a name?

For example, has anyone seen something like: "quqrit" for a 4-level system[1], or "qupit" for a 5-level system[2] ? 1 From "quad" or "quart" since "tetra" would be qutrit, which is already a 3-level ...
user1271772's user avatar
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7 votes
1 answer
183 views

In qubit/qudit terms, where is the experimental limit between S=3/2 and 2·S=1/2?

This question is inspired by "What is the difference between a qudit system with d=4 and a two-qubit system?", as an experimental follow-up. Consider for illustration these two particular cases: ...
agaitaarino's user avatar
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14 votes
5 answers
2k views

What is the difference between a qudit system with d=4 and a two-qubit system?

I understand that a qudit is a quantum $d$-state system. If $d=4$, is this exactly the same as a two-qubit system, which also presents $4$ quantum states? The Hilbert space is the same, right? Are ...
Daniel Tordera's user avatar
3 votes
2 answers
545 views

What is the most economical and preferred basis for the qudit?

In Classical Simulation of Quantum Error Correction in a Fibonacci Anyon Code, the authors state on page 2 in section I. Background, A. Topological model: We consider a system supporting nonabelian ...
Rob's user avatar
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3 votes
2 answers
970 views

Is quantum computing limited to a superposition of only two states?

From Wikipedia: A qubit is a two-state quantum system [...] There are two possible outcomes for the measurement of a qubit — usually $0$ and $1$, like a bit. The difference is that whereas the state ...
Sanchayan Dutta's user avatar