Team Constructs Silicon 2-qubit Gate, Enabling Construction of Quantum Computers (phys.org)

monkeyzoo writes: A team at the University of New South Wales (UNSW) in Sydney has made a crucial advance in quantum computing. Their advance, appearing in the journal Nature (abstract), demonstrated a two-qubit logic gate — the central building block of a quantum computer — and, significantly, did it in silicon. This makes the building of a quantum computer much more feasible, since it is based on the same manufacturing technology as today's computer industry. Until now, it had not been possible to make two quantum bits 'talk' to each other — and thereby create a logic gate — using silicon. But the UNSW team — working with Professor Kohei M. Itoh of Japan's Keio University — has done just that for the first time. The result means that all of the physical building blocks for a silicon-based quantum computer have now been successfully constructed, allowing engineers to finally begin the task of designing and building a functioning quantum computer.

Comments

So Quantum Computing is real now?

[lgw]

This step forward makes "quantum computing" real to me. Up till now, it's all been so experimental that it was divorced from engineering, and for me the target of much skepticism. Now that it's being done in silicon, however, it's on its way to being a product. Finally we might get past the hype and see what can actually be delivered!

Re:So Quantum Computing is real now?

[Anonymous Coward]

From the article, I understand that they have managed to entangle 2 particles together in a silicon chip. In a true quantum computer, you want to have much more than 2 particles entangled together. Adding many of those 2-particle-entangled chips isn't going to create a bigger quantum computer.

The hard problem with quantum computers is decoherence. Maintaining 2 particles entangled is easy but maintaining 10 is very hard because the particles naturally tend to "collapse" as soon as they interact with anything in their environment.

As much as this may be a very interesting progress towards building quantum computers, we have yet to solve the problem of maintaining 10, 20 or perhaps 100 qubits in an entangled state.

Re:Well there goes the cipherhood

[monkeyzoo]

Say goodbye to asymmetric encryption.
Symmetric like AES can still survive quantum attacks with a doubling of key length. But all the current asymmetric algorithms are in peril once quantum computers exist.

Re:Well there goes the cipherhood

[Junta]

Of course the issue being that AES isn't useful in many contexts without key exchange, which is generally rooted in asymmetric algorithms. Pre-shared key circumstances exist, but are exceptionally rare and not particularly feasible in most internet contexts.

Such a strategy using username/password as foundation of the strategy can work once a relationship is boot strapped, but no good way to bootstrap a new secure relationship.

Re:Well there goes the cipherhood

[Bob the Super Hamste]

Well AES, Twofish, serpent, etc. were all designed with quantum computers in mind hence the 256 bit key lengths. To brute force with even with quantum computers it takes more energy than can be reasonably harvested from our sun. What I wonder is if there are other weaknesses in symmetric key crypto that can be exploited with quantum computers that aren't a brute force attack. This is where the interesting results will happen.

Translation ...

[DrJimbo]

The real problem with quantum computers is noise and decoherence. To make a practical quantum computer you need three things:

1) Qubits thare are very loosely coupled with the environment so they have a long decoherence time
2) A way of coupling these qubits to each other without destroying (1).
3) A way of reading from and writing to qubits without destroying (1) or (2).

I *think* this paper claims to have solved (2) and (3). I believe (1) had previously been solved by the use of electron spin with atoms of Silicon-28 which this paper uses as well. Do a search for "qubit silicon 28". I think a saw a measured decoherence time of 200 microseconds. This would mean that a calcuation would need to be completed in well under this time in order to not get swamped out by noise from the environment.

Re:Well there goes the cipherhood

[TechyImmigrant]

Say goodbye to asymmetric encryption.
Symmetric like AES can still survive quantum attacks with a doubling of key length. But all the current asymmetric algorithms are in peril once quantum computers exist.

Say hello to quantum encryption to replace some uses of asymmetric algorithms (which are often only used to exchange keys for symmetric algorithms).

The real danger is to public-private key signature algorithms (such as those used to sign certificates). At some point these may need to change to use proof-of-work (e.g., bitcoin) style authentication or other cost prohibitive measures...

No, there are quantum secure public key algorithms. They are around 2X less efficient on key size than ECC. So it's not a huge problem.