While the IBM Quantum Summit and QC Ware's Q2B Silicon Valley Conference dominated the news stream last week, other quantum news is also emerging. Below, we briefly review other highlights of developments in the quantum field.
The first is the findings published last Thursday in the journal Science, where two groups of researchers at Harvard University and Princeton University used the entire molecule as a qubit. The two groups of researchers used optical tweezers to control the calcium fluoride molecule, achieving entanglement. In the journal Nature, a review by D**ide Castelvecchi sums up the two studies well:
*Links:
*Link: Both studies used an array of optical tweezers, with one molecule trapped in each optical tweezer unit. Through laser technology, they cooled molecules to temperatures of tens of micro-kelvin, which is only one millionth of absolute zero. In this state, the molecules are close to complete rest. They can either stop rotating or rotate with just one quantum of angular momentum (known as ), which is the minimum rotational frequency they may have. ”
Both teams represented the | of the qubits with non-rotating molecules0 state, represented by the spinning molecule |1 Status. ”
As a result, there may be one more member in the qubit queue.
Many years ago, there was an attempt to use whole molecules as qubits;These two recent efforts are a major step forward. Of course, there are more and more qubits vying for the market: these include superconductivity, trapped ions, neutral atoms, photonics, silicon spin, diamond vacancies, and topology.
Results of experiments by the Harvard University team. (a) (Above) Average fluorescence image of a 20-position CAF molecular optical tweezers array;(middle) Schematic diagram of the optical tweezers and coordinate system used in the study;(Bottom) shows the relative angle between the applied bias magnetic field and the tweezer array arrangement. The tweezers are photopolarized along the z-axis (perpendicular to the bias magnetic field), and r represents the instantaneous time distance between molecules. (b) The rotational state (N) and the hyperfine state (F) in the basic electronic state of CAF
Molecular quantum computers will be slower than computers using other types of qubits for most applications, the researchers say. However, molecules may be a natural environment for manipulating quantum information using "qubits", and there are three possible states of qubits: |-1⟩、|0 and |+1⟩。This qutrites can provide a method for quantum simulations of complex materials or fundamental forces of physics.
In fact, back in August last year, Peter Chapman, an expert in capture ions and CEO of Ionq, announced that qubits were about to usher in a new paradigm breakthrough.
It's a bit controversial, but I think there are other qubit patterns out there that might be better in the long run. It's just that in the next five to ten years, they won't be where we are now. But if you were to say to me, in 15 or 20 years, which qubit pattern would I probably use?I don't know,Neutral atoms could be an interesting platform at that time, or something else. ”
Also on Thursday, Rigetti Computing unveiled the 9-qubit Novera QPU for direct sales to researchers.
Rigetti reports: "Novera QPU is available at Rigetticom novera order,Prices start at $900,000, shipped within 4-6 weeks after the order is confirmed, shipping and logistics finalized. ”
It's an interesting betIt could be a cautious attempt at the commercial QPU market。Here's a quick summary of Rigetti's use of the new QPU:
The Novera QPU enables general-purpose, gate-based quantum computing that quantum software and algorithm experts can use to prototype and test: (1) hybrid quantum algorithms;(2) Characterization, calibration, and error mitigation;(3) Quantum error correction (QEC) experiments. ”
In addition, organizations looking to develop components of their quantum computing stack can leverage the Novera QPU to accelerate work in the following areas: (1) control electronics and software, (2) QEC decoders, (3) control optimization algorithms, (3) native gate architecture, and (4) measurement and calibration and companion software. ”
This sounds more like a research tool than a commercial component for self-built quantum computing. Rigetti reports that the Novera QPU is manufactured at "Rigetti's FAB-1 facility – the industry's first purpose-built integrated quantum device manufacturing facility."
Here's how Rigetti describes the Novera QPU components:
A puck containing 9-qubit and 5-qubit chips, an interposer, and a printed circuit board to transmit signals to the SMPM connector around the puck's periphery.
Towers suspended from MXCs to connect coaxial cables between PUCK and SMA patch panelsThe tower transfers the cooling power from the MXC to the chip.
A shield around the tower to isolate the chip from infrared radiation and stray magnetic fields.
The payload bracket and signal chain mounted around the tower, including signal conditioning devices such as ferrite isolators, duplexers, filters, and optional quantum limiting amplifiers.
The Novera uses the same architecture as the Rigetti***Ankaa-level architecture, with an adjustable coupler and a square lattice for denser connections and fast 2-qubit operation.
It is worth noting thatSome of the relevant QPU has been commissioned by national laboratories for manufacturing
At the moment, there is a rush to develop quantum algorithms – like Peter Shaw's algorithm, which can be proven to be faster than classical algorithms.
Google reported on such a development in a blog post last week with an article (Exponential Quantum Speedup in Simulating Combined Classical Oscillators).
*Link: The Google team reported the discovery of a new quantum algorithm that offers an exponential advantage for simulating coupled classical harmonic oscillators. These are the most basic and ubiquitous systems in nature and can describe the physical properties of countless natural systems, from electrical circuits and molecular vibrations to bridge mechanics.
Google, in collaboration with scientists at Macquarie University and the University of Toronto, has discovered a "map" that can turn any system involving coupled oscillators into a problem that describes the temporal evolution of quantum systems. Under certain constraints, quantum computers can solve this problem several times faster than classical computers
In addition, the collaborating team used this mapping to prove that any problem that can be effectively solved by quantum algorithms can be reshaped into problems involving coupled oscillator networks, albeit exponentially in number. In addition to uncovering previously unknown application areas of quantum computers,This result also provides a new way to design new quantum algorithms by purely inferring classical systems
A simple example of a harmonic oscillator is a mass of matter attached to a wall with a spring
The system considered experimentally consists of classical harmonic oscillators. An example of a single harmonic oscillator is a block of matter (such as a ball) attached to a spring. If the mass is removed from the resting position, the spring will create a restoring force that pushes or pulls the mass in the opposite direction. This restoring force causes the mass to oscillate back and forth. ”
Now consider a coupling harmonic oscillator, i.e., multiple blocks of matter connected to each other by springs. Moving a block of matter creates an oscillating wave in the system. As we expected, it would become increasingly difficult to simulate the oscillations of a large number of masses on a classical computer. ”
An example of a spring-connected matter system that can be simulated using a quantum algorithm.
Looking to the future, the blogger writes: "We demonstrate that the dynamics of any classical harmonic oscillator system can be understood equivalently as the dynamics of a correspondingly exponentially smaller quantum system." In this way,The analogies we find between classical and quantum systems can be used to build other quantum algorithms, providing exponential speedups
Effective Error Correction Error mitigation may have become a central challenge in quantum computing. Quera, an expert in quantum error correction based on neutral atoms, reported last week that work led by Harvard University in collaboration with Quera, MIT, and NIST UMD has successfully executed large-scale algorithms on error-correcting quantum computers with 48 logical qubits and hundreds of entangled logic operations.
*Links: The researchers listed the following highlights:
The largest logical qubit ever created and entangled, showing a distance of 7, enables the detection and correction of arbitrary errors that occur during the operation of the entangled logic gate (the greater the distance, the greater the resistance to quantum errors). In addition, studies have shown for the first time that increasing the distance does reduce the error rate in logical operations.
48 small logic qubits for executing complex algorithms are implemented, outperforming the same algorithm when using physical qubits.
By controlling 280 physical bits, 40 medium-sized error correction codes were constructed.
Nature reported last week on the work (a logical quantum processor based on reconfigurable atomic arrays). Here's a summary:
We report on the implementation of a programmable quantum processor based on coded logic qubits that can run up to 280 physical qubits. Utilizing logic-level control and a partition architecture in a reconfigurable array of neutral atoms, our system combines high two-qubit gate fidelity, arbitrary connectivity, and fully programmable single-qubit rotation and mid-path readout. By using various types of encoding to run this logic processor, we demonstrate the improvement of two-qubit logic gates by scaling the surface code distance from d = 3 to d = 7, the fabrication of colorcode qubits with break-even fidelity, the fault-tolerant creation of logical GHZ states and feedforward entanglement** transfers, and the operation of 40 color-coded qubits. ”
Finally, using a three-dimensional block, we implement a complex computational sampling circuit with up to 48 logical qubits, which are connected and entangled by 228 logical two-qubit gates and 48 logical CCZ gates. We find that this logical coding greatly improves the performance of the error detection algorithm and outperforms the physical qubit fidelity in both the cross-entropy benchmark and the quantum simulation of fast scrambling codes. ”
The results herald "the arrival of early error-correcting quantum computing and point the way to large-scale logic processors," the researchers said.
*, it should be noted that the optimized controls and enhanced laser power should allow this architecture to reach 10,000 physical bits, so there should be considerable leeway;And, since all control operations are done by laser, it should be possible to use a photonic link to connect the independent hardware.
With this approach, scientists don't need thousands, hundreds of thousands, or millions of physical qubits to correct errors. If this method works, the error correction speed will be greatly accelerated, which is amazing.