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quantum inferiority

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This room is an old room, please go to #quantum_computing:matrix.org | quantum computing, quantum programming, quantum networking Ask questions - there are no stupid QC questions, or tell us what you like and why. 24 Servers

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18 Jun 2022
@seph:ncli-design.comsephCan I ask, what is the big difference between the theory of applying a quantum gate to a state, and sending that state through a quantum channel?08:19:09
@tmonz:matrix.org@tmonz:matrix.orgA gate is usually unitary. So the purity and/or coherence will stay the same. A quantum channel may also describe effects such as spontaneous decay, dephasing, popularizing noise, ... so the range of properties of the output state could be significantly altered. Also, a channel is not necessarily reversible, because it's not necessarily unitary09:23:51
@tmonz:matrix.org@tmonz:matrix.orgA channel is thus a generalisation of gate10:42:30
@tmonz:matrix.org@tmonz:matrix.org Look at typical descriptions.. a gate would be a unitary U that maps rho unto U rho Udag
A channel is more like: sum p_i U_i rho Udag_i ... where p_i is the probability for U_i to occur
10:45:08
@tmonz:matrix.org@tmonz:matrix.orgDephasing may be intuitive. There is (1-p) for the identity operation, and p for the Z gate10:46:07
@tmonz:matrix.org@tmonz:matrix.org With p=0 nothing happens. With p=0.5 "a phase flip occurs" 50% of the time ... if you now sum up the terms, the off-diagonal terms all become zero and you are left with the populations only (a diagonal matrix) but no coherences (off diagonal non zero terms) 10:48:24
@tmonz:matrix.org@tmonz:matrix.orgDoes that help?10:48:33
@tmonz:matrix.org@tmonz:matrix.org* Dephasing channel may be intuitive. It is the sum of doing nothing, and sometimes a phase flip. There is (1-p) for the identity operation, and p for the Z gate12:38:50
@tmonz:matrix.org@tmonz:matrix.org I found that there is sometimes a bit of a clash of "language". In spectroscopy, you would talk about time relative to T2 ... while for quantum info, you would talk about the probability that a phase flip is applied. Both groups talk about the same thing, but in different words 12:40:42
@tmonz:matrix.org@tmonz:matrix.orgIf I recall correctly, (1-2p)=Exp(-t/T2) ... there may be a factor of 2 in the wrong place , but its roughly that12:43:20
@tmonz:matrix.org@tmonz:matrix.orgActually it looks correct. For t to infinity, meaning full dephasing, you get p=0.512:52:15
@seph:ncli-design.comsephSorry, that does help! So it IS a quantum gate in practice, when applying it mathematically, just with fewer constraints as I ubdeestand you.15:06:19
@seph:ncli-design.comseph* Sorry, that does help! So it IS a quantum gate in practice, when applying it mathematically, just with fewer constraints as I understand you.15:06:35
@tmonz:matrix.org@tmonz:matrix.org Well. Up to you whether you call it fewer, or "richer" 16:39:00
@seph:ncli-design.comsephFair enough.16:49:58
@seph:ncli-design.comsephI'm reading up for a information theory exam at the moment, and am having some trouble understanding quantum data compression. Does anyone here have a good grasp of it?16:51:20
@1ethanhansen:matrix.org@1ethanhansen:matrix.orgRedacted or Malformed Event16:59:12
@tmonz:matrix.org@tmonz:matrix.org
In reply to @1ethanhansen:matrix.org
https://www.metaculus.com/questions/11319/quantum-computing-tolerance-5/
wanted to put this here before I forgot about it. Sorry not really related to you question seph :)
not sure where this is going. a higher threshold, for me, just means that on the long run i ideally need less physical qubits to push the effective error to reasonable small numbers down ...
17:34:23
@tmonz:matrix.org@tmonz:matrix.orgbecause few systems have as high error rates as 5% these days. most systems are already better17:34:45
@seph:ncli-design.comseph
In reply to @1ethanhansen:matrix.org
https://www.metaculus.com/questions/11319/quantum-computing-tolerance-5/
wanted to put this here before I forgot about it. Sorry not really related to you question seph :)
No worries :-)
17:35:43
21 Jun 2022
@array:matrix.orgarray@room 16:04:23
@array:matrix.orgarrayFirst off I want to apologize for the lack of upkeep in this room. Its been a while and I appear to be the only one still around with any sort of privileged permissions in this room. I was also unable to contact any of the admin accounts(that still exist) from michelle. Which leaves this room with only one moderator with very little time and no admins what so ever. Seeing that, I decided Im going to take over the room. The way michelle had set up the room permissions allows me to use a manual room upgrade to give myself administrator permissions and, well, upgrade the room. The upgrade itself will also bring a number of improvements.16:04:45
@array:matrix.orgarrayIn case your matrix client does not support tombstone events, you can click here: [put new alias here]16:06:19
@mrtnmrtn:matrix.orgMrtn array: Which room version will you upgrade to? 16:07:55
@mrtnmrtn:matrix.orgMrtnRight strip it off all adresses.16:08:16
@mrtnmrtn:matrix.orgMrtnExcept perhaps the privacytool one, lol.16:08:50
@array:matrix.orgarray * In case your matrix client does not support tombstone events, you can click here: #quantum_computing:matrix.org 16:09:24
@array:matrix.orgarray changed the room topic to "This room is an old room, please go to #quantum_computing:matrix.org quantum computing, quantum programming, quantum networking Ask questions - there are no stupid QC questions, or tell us what you like and why. " from "quantum computing, quantum programming, quantum networking Ask questions - there are no stupid QC questions, or tell us what you like and why. ".16:16:04
@array:matrix.orgarray * First off I want to apologize for the lack of upkeep in this room. Its been a while and I appear to be the only one still around with any sort of privileged permissions in this room. I was also unable to contact any of the admin accounts(that still exist) from michelle. Which leaves this room with only one moderator with very little time and no admins what so ever. Seeing that, I decided Im going to take over the room. The way michelle had set up the room permissions allows me to use a manual room upgrade to give myself administrator permissions and, well, upgrade the room. The upgrade itself will also bring a number of improvements. We will upgrade to room version 9. Also, please note that it can take a bit of time for everything to properly propagate through the matrix network. Should there be anything that doesnt work please wait a few hours and try again, if it still doesnt work, please DM me.16:19:56
@array:matrix.orgarray changed the room topic to "This room is an old room, please go to #quantum_computing:matrix.org | quantum computing, quantum programming, quantum networking Ask questions - there are no stupid QC questions, or tell us what you like and why. " from "This room is an old room, please go to #quantum_computing:matrix.org quantum computing, quantum programming, quantum networking Ask questions - there are no stupid QC questions, or tell us what you like and why. ".16:24:26

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