The Record-Breaking Quantum Logic Gate with 99.9% Precision

August 31, 2016 by Dr. Steve Arar

Researchers have passed an important milestone in building high-precision quantum gates with record-breaking precision of 99.9%

A quantum logic gate developed at Oxford University can create quantum-entangled particles with 99.9% precision.

Researchers at the University of Oxford have passed an important milestone in building high-precision quantum gates with a record-breaking precision of 99.9%.

Considering the fact that, theoretically, we need high-fidelity quantum logic gates with over 99% precision to achieve fault-tolerant quantum computations, this new technology can significantly speed up developing practical quantum computers.

Quantum Computers vs. Classic Computers

Quantum computers are not going to be a replacement for classic computers like the ones you have in your home. However, they obviously hold the potential to marginalize even today’s most powerful computers in solving particular problems. In other words, quantum computers are not generally faster than the classic ones; they are only faster for the type of problems which can utilize the endless possibilities offered by the quantum mechanics.

Quantum computing uses quantum bits or qubits to represent data. While in classical computing each bit is either one or zero, qubits behave quantumly according to the laws of quantum physics.

Due to the superposition phenomenon of quantum mechanics, a qubit can be one, zero, or a superposition of these two states. Superposition means that a quantum system can be in multiple states at the same time. Extending the superposition phenomenon for a general quantum system, we find that an N-qubit system contains as much information as a 2N-bit classical computing system.

We should note that although qubits can assume a superposition of a large number of states, as soon as we measure a qubit, it falls into one of its base states and all the other information carried by the qubit before measuring is lost.


Image courtesy of Jbw2 [CC BY 2.5], via Wikimedia Commons

With many quantum superpositions available, a quantum computer provides computational parallelism in solving complex problems which require us to deal with very large amounts of data.

According to Andrea Morello, professor of electrical engineering and telecommunications at the University of New South Wales, we do not expect a quantum computer to necessarily expedite a single information processing operation. Instead, a quantum computer can exponentially reduce the number of operations required to perform a particular algorithm.

As Chris Ballance, the lead author of the research, explains a quantum computer is fundamentally different from our everyday computers and it is not merely a different technology.

Quantum Entanglement

The new gate is based on putting two atoms in a state of quantum entanglement. Entanglement, which is fundamental to quantum computing, is an extremely strong connection between two quantum particles in a way that the state of particles cannot be described independently of one another.

According to a co-author of the research, Professor David Lucas of Oxford University’s Department of Physics and Balliol College, two entangled particles share a joint quantum state and when we measure a property of one of the particles, we obtain information about the other particle too.

The example of identical twins is a tangible analogy to discuss two entangled particles. A common tale is that identical twins can feel each other’s pain or emotions even from a long distance away. This is representative of what happens for two entangled particles.

In a highly entangled quantum system, a large amount of information is conveyed by the relationship between the entangled particles and you will have to study all of the particles at once to analyze the system.

Quantum Logic Gates

A quantum logic gate receives two independent atoms and puts them in a state of quantum entanglement. The gate precision tells us how well the gate does this. The new gate which has the precision of 99.9% which means that it can successfully generate the entangled particles 999 times out of 1000 and only one of all these experiments lead to qubits which are not correctly entangled.


Image courtesy of Physical Review Letters.

Quantum computation faces many challenges and the technology is still in its infancy. One of these challenges is to build the required quantum logic gates, then we need to develop the techniques which can utilize multiple gates to process data.

As Professor Lucas explains, a precision of 99.9% is theoretically enough to build a quantum computer. However, in practice, it would be very difficult and expensive. He hopes that a future precision of 99.99% will enhance the prospect of a practical quantum computer.

The new method is presented in a paper entitled 'High-Fidelity Quantum Logic Gates Using Trapped-Ion Hyperfine Qubits' in the journal Physical Review Letters.