One often-repeated example illustrates the mind-boggling potential of quantum computing: A machine with 300 quantum bits could simultaneously store more information than the number of particles in the known universe.<\/p>\n
Now process this: Harvard scientists just unveiled a system that was 10 times bigger and the first quantum machine able to operate continuously without restarting.<\/p>\n
In a paper published in the journal Nature<\/a>, the team demonstrated a system of more than 3,000 quantum bits (or qubits) that could run for more than two hours, surmounting a series of technical challenges and representing a significant step toward building the super computers, which could revolutionize science, medicine, finance, and other fields.<\/p>\n \u201cWe demonstrated the continuous operation with a 3,000-qubit system,\u201d said Mikhail Lukin<\/a>, Joshua and Beth Friedman University Professor and co-director of the Quantum Science and Engineering Initiative, and senior author of the new paper. \u201cBut it\u2019s also clear that this approach will work for much larger numbers as well.\u201d<\/p>\n The Harvard-led collaboration included researchers from MIT and was jointly headed by Lukin, Markus Greiner<\/a>, George Vasmer Leverett Professor of Physics, and Vladan Vuletic<\/a>, Lester Wolfe Professor of Physics at MIT. The team conducts research in collaboration with QuEra Computing, a startup company spun out from Harvard-MIT labs.<\/p>\n Conventional computers encode information \u2014 from a video on your phone to the words and images on this page \u2014 in bits with a binary code. Quantum computers use subatomic particles in individual atoms and take advantage of counterintuitive properties of quantum physics to achieve far more processing power.<\/p>\n Binary conventional bits store information as zeros or ones. Qubits can be zero, one, or both at the same time \u2014 and this linear combination of amplitudes is the key to the power of quantum computing.<\/p>\n In conventional computers, doubling the number of bits doubles the processing power; in quantum computers, adding qubits exponentially increases the power because of a process called quantum entanglement.<\/p>\n But realizing large quantum systems has posed major challenges.<\/p>\n Systems of neutral atoms (those with no electrical charge because they have equal numbers of protons and electrons) have emerged as one of the most promising platforms for quantum computers.<\/p>\n But one stubborn problem has been \u201catom loss\u201d \u2014 qubits escaping and losing their coded information. This shortcoming has limited experiments to one-shot efforts in which researchers must pause, reload atoms, and begin again.<\/p>\n \u201cWe\u2019re showing a way where you can insert new atoms as you naturally lose them without destroying the information that\u2019s already in the system.\u201d<\/p>\n Elias Trapp<\/p>\n In the new study, the team devised a system to continually and rapidly resupply qubits using \u201coptical lattice conveyor belts\u201d (laser waves that transport atoms) and \u201coptical tweezers\u201d (laser beams that grab individual atoms and arrange them into grid-like arrays). The system can reload up to 300,000 atoms per second.<\/p>\n \u201cWe\u2019re showing a way where you can insert new atoms as you naturally lose them without destroying the information that\u2019s already in the system,\u201d said Elias Trapp, the paper co-author and a Ph.D. student in the Kenneth C. Griffin School of Arts and Sciences studying physics. \u201cThat really is solving this fundamental bottleneck of atom loss.\u201d<\/p>\n The new system operated an array of more than 3,000 qubits for more than two hours \u2014 and in theory, the researchers said, could continue indefinitely. Over two hours, more than 50 million atoms had cycled through the system.<\/p>\n Lukin added, \u201cThis new kind of continuous operation of the system, involving the ability to rapidly replace lost qubits, can be more important in practice than a specific number of qubits.\u201d<\/p>\n In follow-up experiments, the team plans to apply this approach to perform computations.<\/p>\n Neng-Chun Chiu, study lead author and a Harvard Griffin Ph.D. student in physics, said: \u201cWhat really makes us stand out is the combination of three things \u2014 the scale, preserving the quantum information, and making the whole process fast enough to be useful.\u201d<\/p>\n The new study advances a fast-developing frontier of research. In fact, this week a team from Caltech published a 6,100-qubit system, but it could only run for less than 13 seconds.<\/p>\n