# Qutrits Bring Quantum Computers Closer

#### kdawson posted more than 6 years ago | from the shortcut-through-higher-dimensions dept.

66
KentuckyFC writes *"To do anything useful with quantum logic gates, you need dozens to hundreds of them, all joined together. And because of various errors and problems that creep in, that's more or less impossible with today's technology. Now an Australian group has built and tested logic gates that convert qubits into qutrits (three-level quantum states) before processing and then convert them back again. That makes them far more powerful. The group says that a quantum computer that might require 50 conventional quantum logic gates can now be built with just 9 of the new gates. What's more, the gates process photons using nothing more than standard linear optical components (abstract on the physics arxiv)."*

## Wow (0)

## Anonymous Coward | more than 6 years ago | (#22963968)

## Re:Wow (1)

## adpsimpson (956630) | more than 6 years ago | (#22964064)

...quantum logic gates...logic gates...qubits...qutrirts...quantum states...quantum computer...quantum logic gates...gates...gates...photons...linear optical components...

For some reason, this reminds me of this post [xkcd.com] on about blogs [xkcd.com] on xkcd.

## Re:Wow (2, Informative)

## CogDissident (951207) | more than 6 years ago | (#22964088)

## Re:Wow (1, Funny)

## Anonymous Coward | more than 6 years ago | (#22964420)

A "gate" is roughly the equivalent of a transistor. Kind of. Think of it like a lot of transistors all put togetherAnd a transistor is kind of like a tube. (remember in the 1960s when they replaced all those tube radios with transistor radios?) So really, when it comes right down to it, the Internet IS really a bunch of tubes.

## Re:Wow (0)

## Anonymous Coward | more than 6 years ago | (#22964962)

## Re:Wow (3, Funny)

## peragrin (659227) | more than 6 years ago | (#22964094)

Or maybe the cat will be spinning because someone stapled a piece of bread with jam onto the cat's back.

## Re:Wow (3, Funny)

## scubamage (727538) | more than 6 years ago | (#22964252)

## Re:Wow (1)

## StariVojnik (1267744) | more than 6 years ago | (#22968102)

## Re:Wow (5, Informative)

## hansraj (458504) | more than 6 years ago | (#22964440)

Of course funny things are possible in quantum computing. For example it is possible to make a "square root of not" gate, that when applied *twice* to the qubit |1> produces |0> and vice versa. Applying once creates something else (the square root of not in some sense).

One particularly handy way to think of quantum gates is to think of them as a matrix (operator) that operates on a vector (input qubit) to produce another vector (output qubit) just by multiplication. So if A is some quantum gate (matrix) and u is input qubit (vector) the the output qubit (vector) v = A*u . The matrix A needs to satisfy some technical requirements that gives quantum computing some nice features (like every algorithm is fully reversible and so on), but those details are not needed to get a rough idea.

## Re:Wow (1)

## jbatista (1205630) | more than 6 years ago | (#22964708)

## Re:Wow (1)

## hansraj (458504) | more than 6 years ago | (#22966198)

## Re:Wow (5, Informative)

## grammar fascist (239789) | more than 6 years ago | (#22967240)

Here's some further detail for those interested: the |1> and |0> qubits are actually vectors of probabilities. (Well, probability "amplitudes". More on that later.) The |0> bit means [1 0] and the |1> bit means [0 1]. The "|.>" notation is a bit of convenient shorthand.

If you have two qubits, you'd represent them as |00>, meaning [1 0 0 0]. (That's four possibilities for the qubits, and all the probability mass on the first: both off.) |01> means [0 1 0 0], |000> means [1 0 0 0 0 0 0 0], and so on. Note the exponential growth.

A quantum gate is nothing more than an operator of the same type that governs all discrete quantum system evolution: a unitary matrix. Think of a rotation matrix of rank 2**(number-of-bits), but in complex space. It's

gotto be some kind of rotation - it must preservelength- to preserve the property that the qubit states and combined qubit states are probability (amplitude) distributions.A "square root of NOT", IIRC, is an operator (rotation) that turns [1 0] (or |0>) into [sqrt(1/2) -sqrt(1/2)]. Do it again, and you get [0 1]. Again, and you get [-sqrt(1/2) sqrt(1/2)], and again yields the original [1 0]. (I may have some signs wrong.)

The reason this cycle works at all is that the states aren't

probabilitiesper se, but sort ofsquare rootsof probabilities, which allows them to keep extra information. This is called "phase". Much of the exciting weirdness of computing with quantum gates is that phase isn't strictly real, but in general has imaginary components.The other exciting weirdness is of the massively parallel sort. If I do a computation on [sqrt(1/2) -sqrt(1/2)], it's sort of like doing the same computation on [1 0] and [0 1]

in parallel. The tricky part is that measuring the outcome restricts me to just one of the results! One way to express the dilemma is that I can compute an answer for every possible input simultaneously (which would be great for solving NP problems), but that I can't easilyselect the right answer.Another way to express it is to say that the cat is in a superposition of dead/alive, which will localize when I observe the poor beast.

## amplitude? analog? (1)

## reiisi (1211052) | more than 6 years ago | (#22969324)

(Actually, I guess, if my elliptical thinking here is anywhere close to meaningful, I guess the idea would be that a quantum processor would allow building complex reprogrammable filters (amplifiers) that don't require iterations. (Not talking about the simple analog filters, of course.)

My son seems enamored of analog computing these days. I remember when I was, as well. Maybe, the babbling above being completely wrong notwithstanding, it's a little early to dismiss analog computing as just a failed path in the problem tree.

I really wish I understood what I am not talking about.

## Re:Wow (0)

## Anonymous Coward | more than 6 years ago | (#22970578)

This stuff isn't simple, unfortunately.

## Re:Wow (1)

## dsmall (933970) | more than 6 years ago | (#22972806)

## Re:Wow (1)

## Schraegstrichpunkt (931443) | more than 6 years ago | (#22973722)

## Personal cryptography users should be disappointed (4, Interesting)

## CRCulver (715279) | more than 6 years ago | (#22963974)

Applied Cryptography [amazon.com]was released, we kept hearing about how it would take thousands or millions of years to crack just one PGP message. Now we hear that computers that could break these messages might be relatively just around the corner. It's got to be a real disappointment and source of worry to people who did use PGP to encode the secrets that they are desparate to hide.## Re:Personal cryptography users should be disappoin (1)

## rubycodez (864176) | more than 6 years ago | (#22964534)

## Re:Personal cryptography users should be disappoin (2, Insightful)

## TheRealMindChild (743925) | more than 6 years ago | (#22964620)

## Re:Personal cryptography users should be disappoin (2, Insightful)

## Cheeko (165493) | more than 6 years ago | (#22964666)

The real power of quantum computing will be in factoring primes. Which most certainly will affect public key crypto, but public key was never the FULL solution. Like anything in crypto different problems have different solutions.

Public key crypto is great in the web age because you can use it for establishing connections, exchanging private keys, etc.

One of the first things you learn in any crypto grad class is that creating the crypto schemes is only part of the problem. Creating the usage scheme is the other. Most man in the middle and other such attacks can defeat the algorithms by which we use crypto far easier than we can defeat the encryption itself. (or just social engineer your way past it)

While it does suck a bit that the heyday of public key crypto might come to an end because of quantum computing, some other scheme will take its place. Perhaps someone will come up with a key gen scheme that doesn't rely on the difficulty of factoring large primes and instead some other mathematical relationship that quantum computing won't be able to stop.

Perhaps the optimal solution will be a mix. Perhaps each public key will in fact be 2 operations. One large prime factor to defeat traditional systems, combined with some as yet created scheme that stops quantum systems (but may be easy to beat on a tradition system).

As with all things, crypto will adapt. Perhaps one day we'll figure out a way using quantum mechanics to create true OTP encryption. Maybe 2 entangled particles or something (I know technically this is impossible, but just making the point maybe there's something we don't know yet that will help us in the future implement todays theoretically impossible/infeasible crypto)

## Re:Personal cryptography users should be disappoin (0)

## Anonymous Coward | more than 6 years ago | (#22965264)

So then the attacker uses a quantum system to get past part A, and a traditional system to get part B.

## Re:Personal cryptography users should be disappoin (0)

## Anonymous Coward | more than 6 years ago | (#22965536)

## Re:Personal cryptography users should be disappoin (1)

## asuffield (111848) | more than 6 years ago | (#22966184)

(Emphasis added)

You might die tomorrow. Hurricanes might devastate the western world. Aliens might show up and blow the planet to bits for housing such a greedy, self-centred species. Any number of progressively unlikely things might happen.

There's no real substance to the rumours of encryption-defeating quantum computers - it's a hypothesis somebody proposed a few years ago, which has never been proved or disproved. We don't know anything about it yet.

## Re:Personal cryptography users should be disappoin (1)

## ajs (35943) | more than 6 years ago | (#22966352)

As for quantum computing: don't get your hopes up. There's no proof of concept that shows that QC will ever scale up to practicality. Every 6 months someone announces a "breakthrough" and gains plenty of funding, but in the final analysis, nothing ever comes of it. I'm convince that there are some fundamental things that we don't understand here, and that all we're going to get out of QC is a better understanding of how to scale down existing computational engineering models (which is a good thing, but not the promise of QC).

## Re:Personal cryptography users should be disappoin (1)

## KDR_11k (778916) | more than 6 years ago | (#22967284)

## Linux??? (1, Funny)

## ZenDragon (1205104) | more than 6 years ago | (#22964032)

## Re:Linux??? (5, Funny)

## hansraj (458504) | more than 6 years ago | (#22964300)

## Re:Linux??? (1)

## mlk (18543) | more than 6 years ago | (#22964576)

So like any other computer then?

## Re:Linux??? (2, Funny)

## ZenDragon (1205104) | more than 6 years ago | (#22964598)

## Re:Linux??? (1)

## LrdDimwit (1133419) | more than 6 years ago | (#22965976)

Alright, enough of these qutrit jokes, they're awful.

## Re:Linux??? (0)

## Anonymous Coward | more than 6 years ago | (#22964462)

## Re:Linux??? (1)

## jellomizer (103300) | more than 6 years ago | (#22966548)

## Qutrits? (-1)

## Anonymous Coward | more than 6 years ago | (#22964112)

## convert qubits into qutrits...far more powerful (3, Funny)

## pushing-robot (1037830) | more than 6 years ago | (#22964134)

## Re:convert qubits into qutrits...far more powerful (1, Funny)

## Anonymous Coward | more than 6 years ago | (#22964246)

## Re:convert qubits into qutrits...far more powerful (4, Funny)

## AaxelB (1034884) | more than 6 years ago | (#22964268)

This would have brought many, many more female engineers into the field of computer science (hence accelerating the pace at which computers could do useful things besides transmit, compress, and enhance pornography), except that the same abbreviational logic that turned "binary digit" into "bit" turned "trinary digit" into "tit." This nomenclatural error set computing back nearly three hundred years, and two entire generations of promising computer scientists were lost trying to keep abreast of bad puns.

## Re:convert qubits into qutrits...far more powerful (0)

## Anonymous Coward | more than 6 years ago | (#22965330)

A quantum superposition of a female breast and a man-boob? You only find out which it is until after it's fondled.

*

## Re:convert qubits into qutrits...far more powerful (1)

## Dekker3D (989692) | more than 6 years ago | (#22967018)

## Re:convert qubits into qutrits...far more powerful (1)

## KDR_11k (778916) | more than 6 years ago | (#22967338)

## All they need to do is.. (2, Funny)

## s0litaire (1205168) | more than 6 years ago | (#22964256)

## What it means (3, Informative)

## usul294 (1163169) | more than 6 years ago | (#22964272)

## Re:What it means (1)

## Your.Master (1088569) | more than 6 years ago | (#22965134)

## Re:What it means (5, Informative)

## mblase (200735) | more than 6 years ago | (#22965576)

Think of an SQL database, where a field can be TRUE or FALSE; however, if you didn't set up default values, it can also be NULL, neither true nor false. Or in mathematics, where a value can be GREATER THAN, LESS THAN, or EQUAL TO -- three mutually exclusive states. These aren't circuit-based examples, but it does illustrate how ternary logic can be routinely applied.

## Re:What it means (2, Interesting)

## lenester (625236) | more than 6 years ago | (#22965794)

## Re:What it means (1)

## WhiteDragon (4556) | more than 6 years ago | (#22966852)

## Re:What it means (1)

## Yetihehe (971185) | more than 6 years ago | (#22965200)

## Re:What it means (1)

## Yetihehe (971185) | more than 6 years ago | (#22965226)

0 AND 0 = 0

0 AND 1 = 0

0 AND 2 = 0

1 AND 1 = 1

1 AND 2 = 1

2 AND 2 = 2

0 OR 0 = 0

0 OR 1 = 1

0 OR 2 = 2

1 OR 1 = 1

1 OR 2 = 2

2 OR 2 = 2

Where 0 means no, 1 means maybe, and 2 means yes?

## Re:What it means (0)

## Anonymous Coward | more than 6 years ago | (#22965614)

I haven't RTFA, but I think the idea here is using some algorithm to convert circuits on binary logic to base 3 and back. It is fine to keep thinking in base 2, the final effect is that the hardware to do that is smaller.

## Re:What it means (1)

## samkass (174571) | more than 6 years ago | (#22965796)

Fry: Don't worry, there's no such thing as 2.

There's a lot of different ways to use the extra value. If you treat it as "unknown", or the logical equivalent of NaN, then you can do NOT, AND, and OR with 0's and 1's, then use 2 as an exception case that can propagate.

## Re:What it means (1)

## KDR_11k (778916) | more than 6 years ago | (#22967376)

## Re:What it means (1)

## bh_doc (930270) | more than 6 years ago | (#22969966)

## Is quantuum gate tech the future of computing? (0)

## Anonymous Coward | more than 6 years ago | (#22964306)

## IANAQCRoM (0)

## Anonymous Coward | more than 6 years ago | (#22964318)

## Re:IANAQCRoM (2, Informative)

## Ctrl-Z (28806) | more than 6 years ago | (#22965524)

## I want to play Qutris (1)

## britneys 9th husband (741556) | more than 6 years ago | (#22964334)

## Trinary Code (1)

## scubamage (727538) | more than 6 years ago | (#22964426)

## Re:Trinary Code (1)

## kalirion (728907) | more than 6 years ago | (#22965546)

## Qubits? Qutrits? BAH! (1)

## KC7GR (473279) | more than 6 years ago | (#22965144)

## I'm looking forward to this. (1)

## rejecting (824821) | more than 6 years ago | (#22965230)

## Australian? Logic? (0)

## Anonymous Coward | more than 6 years ago | (#22965984)

Does. . .not. . .compute. . .

## Riiiiiiight (1)

## Chris Mattern (191822) | more than 6 years ago | (#22966008)

## Re:Riiiiiiight (1)

## hansraj (458504) | more than 6 years ago | (#22966262)

## More science sensationalism (1)

## ajayg (122305) | more than 6 years ago | (#22966778)

## The day is mine!!! (1)

## 3-State Bit (225583) | more than 6 years ago | (#22968400)

I'm a visionary!

3-State Bit [slashdot.org]## Trinary? (1)

## Shadow-isoHunt (1014539) | more than 6 years ago | (#22968728)

## Quantum Python (1)

## tsotha (720379) | more than 6 years ago | (#22970686)

we were happy to have them!