Until recently measuring a 27-dimensional quantum state would have been a time-consuming, multistage process using a technique called quantum tomography, which is similar to creating a 3D image from many 2D ones.
Researchers at the University of Rochester have been able to apply a recently developed, alternative method called direct measurement to do this in a single experiment with no post-processing.
The work is of interest because fast, accurate and efficient methods for characterizing high-dimensional states like this could be central in developing high security quantum communications systems, as well as to probe our fundamental understanding of quantum mechanics.
The work was published this week in Nature Communications by a team of researchers from the University of Rochester and the University of Glasgow. In the paper they demonstrate direct measurements of the quantum state associated with the orbital-angular momentum.
"Our work shows that direct measurement offers an exciting alternative to quantum tomography," said Robert Boyd, Professor of Optics and Physics at the
University of Rochester and Canada Excellence Research Chair in Quantum Nonlinear Optics at the University of Ottawa. "As the field of quantum information continues to advance, we expect direct measurement to play an increasingly important role in this." Boyd added that although it is unclear exactly how much more efficient direct measurement is compared to quantum tomography, the lack of post-processing is a major factor in speeding-up direct measurements.
The direct measurement technique offers a way to directly determine the state of a quantum system. It was first developed in 2011 by scientists at the National Research Council Canada, who used it to determine the position and momentum of photons. Last year, a group of Rochester/Ottawa researchers led by Boyd showed that direct measurement could be applied to measure the polarization states of light. The new paper is the first time this method has been applied to a discrete, high dimensional system.
Such direct measurements of the wavefunction might have appeared to be ruled out by the uncertainty principle – the idea that certain properties of a quantum system could be known with precision only if other properties were known poorly. However, direct measurement involves a "trick" that makes it possible.
Direct measurements consists of two types of measurements performed one after the other, first a "weak" measurement followed by a "strong" measurement. In quantum mechanics the act of measuring a quantum state disturbs it irreversibly, a phenomenon referred to as collapse of the wavefunction. The trick lies with the first measurement being so gentle that it only slightly disturbs the system and does not cause the wavefunction to collapse.
"It is sort of like peeking into the box to see if Schrodinger's cat is alive, without fully opening the box," said lead author Dr. Mehul Malik, currently a post-doctoral research fellow at the University of Vienna and who was a Ph.D. in Boyd's group when the work was performed. "The weak measurement is essentially a bad measurement, which leaves you mostly uncertain about whether the cat is alive or dead. It does, however¬, give partial information on the health of the cat, which when repeated many times can lead to near certain information as to whether the cat is alive or dead." Malik adds that the beauty of the weak measurement is that it does not destroy the system, unlike most standard measurements of a quantum system, allowing a subsequent measurement—the "strong" measurement of the other variable.
This sequence of weak and strong measurements is then repeated for multiple identically prepared quantum systems, until the wave function is known with the required precision.
Ph.D. student Mohammad Mirhosseini was also part of the Rochester team. Other collaborators included Professor Miles Padgett and Martin Lavery from the University of Glasgow, UK, and Dr. Jonathan Leach, from Heriot-Watt University, Edinburgh, UK.
About the University of Rochester
The University of Rochester is one of the nation's leading private universities. Located in Rochester, N.Y., the University gives students exceptional opportunities for interdisciplinary study and close collaboration with faculty through its unique cluster-based curriculum. Its College, School of Arts and Sciences, and Hajim School of Engineering and Applied Sciences are complemented by its Eastman School of Music, Simon School of Business, Warner School of Education, Laboratory for Laser Energetics, School of Medicine and Dentistry, School of Nursing, Eastman Institute for Oral Health, and the Memorial Art Gallery.
Leonor Sierra | EurekAlert!
Suzaku, Herschel link a black-hole 'wind' to a galactic gush of star-forming gas
26.03.2015 | NASA/Goddard Space Flight Center
Tiny Bio-Robot Is a Germ Suited-Up with Graphene Quantum Dots
25.03.2015 | University of Illinois at Chicago
In an experiment at the Department of Energy's SLAC National Accelerator Laboratory, scientists precisely measured the temperature and structure of aluminum as...
The IPH presents a solution at HANNOVER MESSE 2015 to make ship traffic more reliable while decreasing the maintenance costs at the same time. In cooperation with project partners, the research institute from Hannover, Germany, has developed a sensor system which continuously monitors the condition of the marine gearbox, thus preventing breakdowns. Special feature: the monitoring system works wirelessly and energy-autonomously. The required electrical power is generated where it is needed – directly at the sensor.
As well as cars need to be certified regularly (in Germany by the TÜV – Technical Inspection Association), ships need to be inspected – if the powertrain stops...
When an earthquake hits, the faster first responders can get to an impacted area, the more likely infrastructure--and lives--can be saved.
The Atlantic overturning is one of Earth’s most important heat transport systems, pumping warm water northwards and cold water southwards. Also known as the Gulf Stream system, it is responsible for the mild climate in northwestern Europe.
Scientists now found evidence for a slowdown of the overturning – multiple lines of observation suggest that in recent decades, the current system has been...
Because they are regularly subjected to heavy vehicle traffic, emissions, moisture and salt, above- and underground parking garages, as well as bridges, frequently experience large areas of corrosion. Most inspection systems to date have only been capable of inspecting smaller surface areas.
From April 13 to April 17 at the Hannover Messe (hall 2, exhibit booth C16), engineers from the Fraunhofer Institute for Nondestructive Testing IZFP will be...
25.03.2015 | Event News
19.03.2015 | Event News
17.03.2015 | Event News
26.03.2015 | Trade Fair News
26.03.2015 | Trade Fair News
26.03.2015 | Life Sciences